Add readme for the hello-world example
Add readme for the hello-world example

Closes #1070.

RubikonAlpha/RIOT,sgso/RIOT,abkam07/RIOT,ntrtrung/RIOT,watr-li/RIOT,adrianghc/RIOT,mfrey/RIOT,asanka-code/RIOT,sgso/RIOT,kaleb-himes/RIOT,cladmi/RIOT,sgso/RIOT,RBartz/RIOT,jfischer-phytec-iot/RIOT,rajma996/RIOT,ant9000/RIOT,binarylemon/RIOT,abp719/RIOT,bartfaizoltan/RIOT,herrfz/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,stevenj/RIOT,miri64/RIOT,fnack/RIOT,kaspar030/RIOT,malosek/RIOT,d00616/RIOT,openkosmosorg/RIOT,kb2ma/RIOT,DipSwitch/RIOT,mziegert/RIOT,khhhh/RIOT,alignan/RIOT,haoyangyu/RIOT,OTAkeys/RIOT,latsku/RIOT,ant9000/RIOT,BytesGalore/RIOT,changbiao/RIOT,avmelnikoff/RIOT,daniel-k/RIOT,Darredevil/RIOT,Hyungsin/RIOT-OS,tfar/RIOT,changbiao/RIOT,marcosalm/RIOT,Osblouf/RIOT,backenklee/RIOT,emmanuelsearch/RIOT,beurdouche/RIOT,authmillenon/RIOT,watr-li/RIOT,kerneltask/RIOT,rfuentess/RIOT,cladmi/RIOT,ximus/RIOT,yogo1212/RIOT,avmelnikoff/RIOT,ros2/ros2_embedded_riot,TobiasFredersdorf/RIOT,basilfx/RIOT,wentaoshang/RIOT,thomaseichinger/RIOT,herrfz/RIOT,alex1818/RIOT,lazytech-org/RIOT,josephnoir/RIOT,khhhh/RIOT,jhollister/RIOT,LudwigOrtmann/RIOT,josephnoir/RIOT,msolters/RIOT,Yonezawa-T2/RIOT,Hyungsin/RIOT-OS,koenning/RIOT,latsku/RIOT,miri64/RIOT,changbiao/RIOT,MarkXYang/RIOT,asanka-code/RIOT,katezilla/RIOT,authmillenon/RIOT,chris-wood/RIOT,kYc0o/RIOT,avmelnikoff/RIOT,changbiao/RIOT,stevenj/RIOT,koenning/RIOT,EmuxEvans/RIOT,locicontrols/RIOT,MarkXYang/RIOT,brettswann/RIOT,emmanuelsearch/RIOT,thomaseichinger/RIOT,binarylemon/RIOT,gebart/RIOT,rfswarm2/RIOT,d00616/RIOT,plushvoxel/RIOT,MarkXYang/RIOT,josephnoir/RIOT,watr-li/RIOT,MohmadAyman/RIOT,thomaseichinger/RIOT,gebart/RIOT,FrancescoErmini/RIOT,tdautc19841202/RIOT,immesys/RiSyn,adjih/RIOT,A-Paul/RIOT,adjih/RIOT,MonsterCode8000/RIOT,wentaoshang/RIOT,attdona/RIOT,changbiao/RIOT,herrfz/RIOT,dhruvvyas90/RIOT,sumanpanchal/RIOT,chris-wood/RIOT,kaleb-himes/RIOT,hamilton-mote/RIOT-OS,MonsterCode8000/RIOT,LudwigOrtmann/RIOT,kushalsingh007/RIOT,abp719/RIOT,LudwigKnuepfer/RIOT,jbeyerstedt/RIOT-OTA-update,Yonezawa-T2/RIOT,asanka-code/RIOT,brettswann/RIOT,lebrush/RIOT,basilfx/RIOT,hamilton-mote/RIOT-OS,gautric/RIOT,thiagohd/RIOT,Lotterleben/RIOT,biboc/RIOT,chris-wood/RIOT,herrfz/RIOT,jhollister/RIOT,FrancescoErmini/RIOT,herrfz/RIOT-old,1blankz7/RIOT,jfischer-phytec-iot/RIOT,immesys/RiSyn,abp719/RIOT,hamilton-mote/RIOT-OS,yogo1212/RIOT,binarylemon/RIOT,Osblouf/RIOT,JensErdmann/RIOT,ros2/ros2_embedded_riot,khhhh/RIOT,abp719/RIOT,haoyangyu/RIOT,ks156/RIOT,gautric/RIOT,mtausig/RIOT,adrianghc/RIOT,ros2/ros2_embedded_riot,OlegHahm/RIOT,beurdouche/RIOT,FrancescoErmini/RIOT,tfar/RIOT,jbeyerstedt/RIOT-OTA-update,rousselk/RIOT,ks156/RIOT,daniel-k/RIOT,jferreir/RIOT,asanka-code/RIOT,thiagohd/RIOT,neiljay/RIOT,avmelnikoff/RIOT,khhhh/RIOT,altairpearl/RIOT,abkam07/RIOT,stevenj/RIOT,lebrush/RIOT,shady33/RIOT,tfar/RIOT,dailab/RIOT,attdona/RIOT,jbeyerstedt/RIOT-OTA-update,kushalsingh007/RIOT,patkan/RIOT,yogo1212/RIOT,kYc0o/RIOT,OlegHahm/RIOT,roberthartung/RIOT,benoit-canet/RIOT,BytesGalore/PetersRIOT,sumanpanchal/RIOT,mziegert/RIOT,thiagohd/RIOT,thomaseichinger/RIOT,rakendrathapa/RIOT,jasonatran/RIOT,lebrush/RIOT,binarylemon/RIOT,chris-wood/RIOT,kaleb-himes/RIOT,lazytech-org/RIOT,Josar/RIOT,biboc/RIOT,Lexandro92/RIOT-CoAP,brettswann/RIOT,benoit-canet/RIOT,marcosalm/RIOT,msolters/RIOT,plushvoxel/RIOT,centurysys/RIOT,rousselk/RIOT,bartfaizoltan/RIOT,kerneltask/RIOT,kaleb-himes/RIOT,1blankz7/RIOT,MohmadAyman/RIOT,RIOT-OS/RIOT,BytesGalore/PetersRIOT,katezilla/RIOT,emmanuelsearch/RIOT,dkm/RIOT,patkan/RIOT,beurdouche/RIOT,brettswann/RIOT,Hyungsin/RIOT-OS,abkam07/RIOT,ant9000/RIOT,altairpearl/RIOT,katezilla/RIOT,aeneby/RIOT,OTAkeys/RIOT,kbumsik/RIOT,backenklee/RIOT,arvindpdmn/RIOT,nsol-nmsu/RIOT,sgso/RIOT,alex1818/RIOT,Josar/RIOT,herrfz/RIOT-old,katezilla/RIOT,MohmadAyman/RIOT,jferreir/RIOT,MonsterCode8000/RIOT,mfrey/RIOT,authmillenon/RIOT,PSHIVANI/Riot-Code,patkan/RIOT,wentaoshang/RIOT,msolters/RIOT,mtausig/RIOT,Lotterleben/RIOT,ximus/RIOT,ant9000/RIOT,lazytech-org/RIOT,immesys/RiSyn,rakendrathapa/RIOT,ntrtrung/RIOT,Yonezawa-T2/RIOT,jferreir/RIOT,spium/IoT-RIOT,Lotterleben/RIOT,Osblouf/RIOT,LudwigKnuepfer/RIOT,dailab/RIOT,bartfaizoltan/RIOT,l3nko/RIOT,BytesGalore/RIOT,centurysys/RIOT,daniel-k/RIOT,khhhh/RIOT,kerneltask/RIOT,authmillenon/RIOT,Lotterleben/RIOT,luciotorre/RIOT,tdautc19841202/RIOT,ros2/ros2_embedded_riot,abkam07/RIOT,toonst/RIOT,rfswarm/RIOT,syin2/RIOT,koenning/RIOT,benoit-canet/RIOT,jfischer-phytec-iot/RIOT,kerneltask/RIOT,kaspar030/RIOT,toonst/RIOT,dailab/RIOT,gbarnett/RIOT,backenklee/RIOT,miri64/RIOT,altairpearl/RIOT,patkan/RIOT,openkosmosorg/RIOT,smlng/RIOT,jbeyerstedt/RIOT-OTA-update,Ell-i/RIOT,Lotterleben/RIOT,authmillenon/RIOT,jremmert-phytec-iot/RIOT,ximus/RIOT,OTAkeys/RIOT,thiagohd/RIOT,bartfaizoltan/RIOT,BytesGalore/RIOT,kbumsik/RIOT,biboc/RIOT,thiagohd/RIOT,jasonatran/RIOT,tdautc19841202/RIOT,DipSwitch/RIOT,openkosmosorg/RIOT,DipSwitch/RIOT,avmelnikoff/RIOT,kaleb-himes/RIOT,BytesGalore/PetersRIOT,RubikonAlpha/RIOT,abkam07/RIOT,malosek/RIOT,rakendrathapa/RIOT,phiros/RIOT,thiagohd/RIOT,altairpearl/RIOT,Lexandro92/RIOT-CoAP,fnack/RIOT,kaspar030/RIOT,dkm/RIOT,kYc0o/RIOT,jremmert-phytec-iot/RIOT,BytesGalore/PetersRIOT,patkan/RIOT,ximus/RIOT,lazytech-org/RIOT,rajma996/RIOT,jfischer-phytec-iot/RIOT,luciotorre/RIOT,Osblouf/RIOT,toonst/RIOT,OTAkeys/RIOT,basilfx/RIOT,gbarnett/RIOT,gebart/RIOT,ros2/ros2_embedded_riot,LudwigKnuepfer/RIOT,l3nko/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,locicontrols/RIOT,luciotorre/RIOT,ks156/RIOT,alignan/RIOT,patkan/RIOT,tdautc19841202/RIOT,RBartz/RIOT,miri64/RIOT,aeneby/RIOT,tdautc19841202/RIOT,locicontrols/RIOT,d00616/RIOT,rfuentess/RIOT,hamilton-mote/RIOT-OS,MohmadAyman/RIOT,rousselk/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,rajma996/RIOT,cladmi/RIOT,watr-li/RIOT,lebrush/RIOT,Josar/RIOT,herrfz/RIOT,AnonMall/RIOT,benoit-canet/RIOT,rousselk/RIOT,spium/IoT-RIOT,TobiasFredersdorf/RIOT,toonst/RIOT,neiljay/RIOT,latsku/RIOT,spium/IoT-RIOT,josephnoir/RIOT,tdautc19841202/RIOT,l3nko/RIOT,robixnai/RIOT,LudwigKnuepfer/RIOT,automote/RIOT,alex1818/RIOT,rakendrathapa/RIOT,haoyangyu/RIOT,immesys/RiSyn,rfuentess/RIOT,MarkXYang/RIOT,beurdouche/RIOT,basilfx/RIOT,katezilla/RIOT,adrianghc/RIOT,RIOT-OS/RIOT,yogo1212/RIOT,koenning/RIOT,PSHIVANI/Riot-Code,d00616/RIOT,jremmert-phytec-iot/RIOT,binarylemon/RIOT,jremmert-phytec-iot/RIOT,rakendrathapa/RIOT,d00616/RIOT,EmuxEvans/RIOT,adrianghc/RIOT,zhuoshuguo/RIOT,rfswarm2/RIOT,backenklee/RIOT,dailab/RIOT,ximus/RIOT,stevenj/RIOT,syin2/RIOT,locicontrols/RIOT,neumodisch/RIOT,gautric/RIOT,cladmi/RIOT,jhollister/RIOT,kerneltask/RIOT,shady33/RIOT,dhruvvyas90/RIOT,zhuoshuguo/RIOT,smlng/RIOT,sumanpanchal/RIOT,abp719/RIOT,aeneby/RIOT,Ell-i/RIOT,l3nko/RIOT,asanka-code/RIOT,mziegert/RIOT,wentaoshang/RIOT,arvindpdmn/RIOT,attdona/RIOT,dailab/RIOT,zhuoshuguo/RIOT,abkam07/RIOT,kb2ma/RIOT,EmuxEvans/RIOT,arvindpdmn/RIOT,josephnoir/RIOT,Ell-i/RIOT,chris-wood/RIOT,sumanpanchal/RIOT,malosek/RIOT,plushvoxel/RIOT,rajma996/RIOT,aeneby/RIOT,roberthartung/RIOT,sgso/RIOT,rfuentess/RIOT,rajma996/RIOT,OlegHahm/RIOT,malosek/RIOT,roberthartung/RIOT,backenklee/RIOT,immesys/RiSyn,1blankz7/RIOT,robixnai/RIOT,x3ro/RIOT,ros2/ros2_embedded_riot,ThanhVic/RIOT,Josar/RIOT,A-Paul/RIOT,Darredevil/RIOT,PSHIVANI/Riot-Code,MonsterCode8000/RIOT,EmuxEvans/RIOT,mfrey/RIOT,phiros/RIOT,rajma996/RIOT,stevenj/RIOT,openkosmosorg/RIOT,neumodisch/RIOT,jferreir/RIOT,Lexandro92/RIOT-CoAP,MonsterCode8000/RIOT,gbarnett/RIOT,toonst/RIOT,dhruvvyas90/RIOT,miri64/RIOT,MonsterCode8000/RIOT,phiros/RIOT,locicontrols/RIOT,ros2/ros2_embedded_riot,zhuoshuguo/RIOT,A-Paul/RIOT,EmuxEvans/RIOT,Ell-i/RIOT,dhruvvyas90/RIOT,RIOT-OS/RIOT,emmanuelsearch/RIOT,alex1818/RIOT,Yonezawa-T2/RIOT,RubikonAlpha/RIOT,rfswarm/RIOT,haoyangyu/RIOT,x3ro/RIOT,herrfz/RIOT,rfswarm/RIOT,abp719/RIOT,changbiao/RIOT,Lexandro92/RIOT-CoAP,mziegert/RIOT,spium/IoT-RIOT,JensErdmann/RIOT,ThanhVic/RIOT,jhollister/RIOT,dkm/RIOT,syin2/RIOT,dkm/RIOT,kbumsik/RIOT,Darredevil/RIOT,automote/RIOT,jhollister/RIOT,shady33/RIOT,kYc0o/RIOT,spium/IoT-RIOT,jhollister/RIOT,RubikonAlpha/RIOT,neiljay/RIOT,jfischer-phytec-iot/RIOT,khhhh/RIOT,stevenj/RIOT,kbumsik/RIOT,Osblouf/RIOT,kb2ma/RIOT,neiljay/RIOT,msolters/RIOT,OlegHahm/RIOT,neumodisch/RIOT,neumodisch/RIOT,bartfaizoltan/RIOT,OTAkeys/RIOT,beurdouche/RIOT,chris-wood/RIOT,latsku/RIOT,JensErdmann/RIOT,alignan/RIOT,LudwigOrtmann/RIOT,latsku/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,d00616/RIOT,RubikonAlpha/RIOT,robixnai/RIOT,phiros/RIOT,Lexandro92/RIOT-CoAP,TobiasFredersdorf/RIOT,sumanpanchal/RIOT,nsol-nmsu/RIOT,DipSwitch/RIOT,zhuoshuguo/RIOT,lebrush/RIOT,marcosalm/RIOT,attdona/RIOT,shady33/RIOT,rfswarm/RIOT,PSHIVANI/Riot-Code,rousselk/RIOT,daniel-k/RIOT,kushalsingh007/RIOT,rfswarm2/RIOT,LudwigOrtmann/RIOT,locicontrols/RIOT,MarkXYang/RIOT,robixnai/RIOT,Lotterleben/RIOT,neumodisch/RIOT,yogo1212/RIOT,MohmadAyman/RIOT,ntrtrung/RIOT,benoit-canet/RIOT,wentaoshang/RIOT,Hyungsin/RIOT-OS,JensErdmann/RIOT,mtausig/RIOT,smlng/RIOT,x3ro/RIOT,Hyungsin/RIOT-OS,syin2/RIOT,EmuxEvans/RIOT,phiros/RIOT,kYc0o/RIOT,plushvoxel/RIOT,centurysys/RIOT,msolters/RIOT,dhruvvyas90/RIOT,kushalsingh007/RIOT,yogo1212/RIOT,RIOT-OS/RIOT,malosek/RIOT,kushalsingh007/RIOT,mfrey/RIOT,robixnai/RIOT,FrancescoErmini/RIOT,immesys/RiSyn,alex1818/RIOT,gbarnett/RIOT,altairpearl/RIOT,jbeyerstedt/RIOT-OTA-update,mziegert/RIOT,haoyangyu/RIOT,ks156/RIOT,ThanhVic/RIOT,Yonezawa-T2/RIOT,ntrtrung/RIOT,arvindpdmn/RIOT,gautric/RIOT,cladmi/RIOT,FrancescoErmini/RIOT,MohmadAyman/RIOT,RBartz/RIOT,BytesGalore/PetersRIOT,hamilton-mote/RIOT-OS,plushvoxel/RIOT,jferreir/RIOT,rfswarm/RIOT,AnonMall/RIOT,robixnai/RIOT,rfswarm2/RIOT,TobiasFredersdorf/RIOT,fnack/RIOT,biboc/RIOT,nsol-nmsu/RIOT,koenning/RIOT,wentaoshang/RIOT,tfar/RIOT,gbarnett/RIOT,dkm/RIOT,jasonatran/RIOT,alex1818/RIOT,Darredevil/RIOT,FrancescoErmini/RIOT,lazytech-org/RIOT,jasonatran/RIOT,kbumsik/RIOT,Darredevil/RIOT,Osblouf/RIOT,centurysys/RIOT,RubikonAlpha/RIOT,locicontrols/RIOT,bartfaizoltan/RIOT,A-Paul/RIOT,AnonMall/RIOT,roberthartung/RIOT,zhuoshuguo/RIOT,attdona/RIOT,adjih/RIOT,l3nko/RIOT,ThanhVic/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,thomaseichinger/RIOT,LudwigOrtmann/RIOT,Josar/RIOT,benoit-canet/RIOT,marcosalm/RIOT,Ell-i/RIOT,adrianghc/RIOT,dhruvvyas90/RIOT,jremmert-phytec-iot/RIOT,ximus/RIOT,gebart/RIOT,kushalsingh007/RIOT,kaspar030/RIOT,AnonMall/RIOT,centurysys/RIOT,BytesGalore/RIOT,1blankz7/RIOT,arvindpdmn/RIOT,smlng/RIOT,herrfz/RIOT-old,LudwigOrtmann/RIOT,syin2/RIOT,BytesGalore/PetersRIOT,l3nko/RIOT,BytesGalore/PetersRIOT,kaspar030/RIOT,1blankz7/RIOT,ks156/RIOT,marcosalm/RIOT,A-Paul/RIOT,JensErdmann/RIOT,luciotorre/RIOT,sgso/RIOT,rakendrathapa/RIOT,automote/RIOT,x3ro/RIOT,PSHIVANI/Riot-Code,DipSwitch/RIOT,spium/IoT-RIOT,emmanuelsearch/RIOT,brettswann/RIOT,roberthartung/RIOT,mziegert/RIOT,Darredevil/RIOT,emmanuelsearch/RIOT,AnonMall/RIOT,daniel-k/RIOT,malosek/RIOT,automote/RIOT,basilfx/RIOT,alignan/RIOT,nsol-nmsu/RIOT,openkosmosorg/RIOT,rfswarm2/RIOT,LudwigKnuepfer/RIOT,fnack/RIOT,BytesGalore/RIOT,TobiasFredersdorf/RIOT,AnonMall/RIOT,koenning/RIOT,gautric/RIOT,herrfz/RIOT-old,RIOT-OS/RIOT,smlng/RIOT,binarylemon/RIOT,rfswarm2/RIOT,JensErdmann/RIOT,phiros/RIOT,ntrtrung/RIOT,ThanhVic/RIOT,watr-li/RIOT,kb2ma/RIOT,RBartz/RIOT,Lotterleben/RIOT,kb2ma/RIOT,neumodisch/RIOT,RBartz/RIOT,rousselk/RIOT,daniel-k/RIOT,msolters/RIOT,haoyangyu/RIOT,MarkXYang/RIOT,lebrush/RIOT,jremmert-phytec-iot/RIOT,marcosalm/RIOT,watr-li/RIOT,gebart/RIOT,adjih/RIOT,mtausig/RIOT,fnack/RIOT,nsol-nmsu/RIOT,PSHIVANI/Riot-Code,shady33/RIOT,luciotorre/RIOT,1blankz7/RIOT,x3ro/RIOT,herrfz/RIOT-old,attdona/RIOT,authmillenon/RIOT,fnack/RIOT,ThanhVic/RIOT,mtausig/RIOT,jferreir/RIOT,ant9000/RIOT,mfrey/RIOT,neiljay/RIOT,adjih/RIOT,tfar/RIOT,gbarnett/RIOT,sumanpanchal/RIOT,OlegHahm/RIOT,luciotorre/RIOT,aeneby/RIOT,arvindpdmn/RIOT,automote/RIOT,DipSwitch/RIOT,shady33/RIOT,ntrtrung/RIOT,openkosmosorg/RIOT,Yonezawa-T2/RIOT,altairpearl/RIOT,alignan/RIOT,biboc/RIOT,asanka-code/RIOT,latsku/RIOT,centurysys/RIOT,Lexandro92/RIOT-CoAP,automote/RIOT,rfuentess/RIOT,brettswann/RIOT,jasonatran/RIOT,RBartz/RIOT,rfswarm/RIOT