add HACKING.rst: style guide
add HACKING.rst: style guide

Signed-off-by: Isaku Yamahata <4b3abd66323411eeceff090ab3754dd766fc4b25@valinux.co.jp>
Signed-off-by: FUJITA Tomonori <93dac1fe9c4b2a3957982200319981492ad4976e@lab.ntt.co.jp>

pichuang/ryu,jkoelker/ryu,lzppp/mylearning,haniehrajabi/ryu,osrg/ryu,openvapour/ryu,iwaseyusuke/ryu,shinpeimuraoka/ryu,zyq001/ryu,muzixing/ryu,gareging/SDN_Framework,elahejalalpour/ELRyu,John-Lin/ryu,pichuang/ryu,hisaharu/ryu,unifycore/ryu,yamada-h/ryu,lagopus/ryu-lagopus-ext,alanquillin/ryu,alanquillin/ryu,ynkjm/ryu,TakeshiTseng/ryu,habibiefaried/ryu,citrix-openstack-build/ryu,StephenKing/summerschool-2015-ryu,Tejas-Subramanya/RYU_MEC,citrix-openstack/build-ryu,diogommartins/ryu,Tejas-Subramanya/RYU_MEC,ttsubo/ryu,openvapour/ryu,muzixing/ryu,gareging/SDN_Framework,ysywh/ryu,elahejalalpour/ELRyu,shinpeimuraoka/ryu,openvapour/ryu,takahashiminoru/ryu,evanscottgray/ryu,StephenKing/ryu,zyq001/ryu,OpenState-SDN/ryu,torufuru/OFPatchPanel,ttsubo/ryu,takahashiminoru/ryu,fkakuma/ryu,OpenState-SDN/ryu,jalilm/ryu,ttsubo/ryu,openvapour/ryu,shinpeimuraoka/ryu,osrg/ryu,StephenKing/ryu,sivaramakrishnansr/ryu,ysywh/ryu,jkoelker/ryu,jalilm/ryu,lzppp/mylearning,iwaseyusuke/ryu,o3project/ryu-oe,lagopus/ryu-lagopus-ext,Zouyiran/ryu,umkcdcrg01/ryu_openflow,iwaseyusuke/ryu,lagopus/ryu-lagopus-ext,iwaseyusuke/ryu,jalilm/ryu,torufuru/OFPatchPanel,mikhaelharswanto/ryu,takahashiminoru/ryu,sivaramakrishnansr/ryu,fujita/ryu,jalilm/ryu,StephenKing/ryu,ysywh/ryu,TakeshiTseng/ryu,gopchandani/ryu,Tejas-Subramanya/RYU_MEC,citrix-openstack-build/ryu,umkcdcrg01/ryu_openflow,fujita/ryu,muzixing/ryu,John-Lin/ryu,jazzmes/ryu,ynkjm/ryu,habibiefaried/ryu,OpenState-SDN/ryu,darjus-amzn/ryu,fkakuma/ryu,unifycore/ryu,TakeshiTseng/ryu,John-Lin/ryu,alanquillin/ryu,alanquillin/ryu,lagopus/ryu-lagopus-ext,hisaharu/ryu,Zouyiran/ryu,gopchandani/ryu,lzppp/mylearning,zyq001/ryu,lagopus/ryu-lagopus-ext,ntts-clo/ryu,lsqtongxin/ryu,ynkjm/ryu,lsqtongxin/ryu,Zouyiran/ryu,zangree/ryu,fujita/ryu,citrix-openstack/build-ryu,umkcdcrg01/ryu_openflow,John-Lin/ryu,StephenKing/summerschool-2015-ryu,ntts-clo/mld-ryu,ntts-clo/mld-ryu,yamt/ryu,habibiefaried/ryu,OpenState-SDN/ryu,lzppp/mylearning,darjus-amzn/ryu,zangree/ryu,castroflavio/ryu,elahejalalpour/ELRyu,alyosha1879/ryu,StephenKing/summerschool-2015-ryu,haniehrajabi/ryu,fujita/ryu,StephenKing/ryu,gareging/SDN_Framework,TakeshiTseng/ryu,takahashiminoru/ryu,o3project/ryu-oe,fkakuma/ryu,pichuang/ryu,darjus-amzn/ryu,haniehrajabi/ryu,muzixing/ryu,lsqtongxin/ryu,lsqtongxin/ryu,umkcdcrg01/ryu_openflow,castroflavio/ryu,gopchandani/ryu,Zouyiran/ryu,pichuang/ryu,fkakuma/ryu,torufuru/oolhackathon,diogommartins/ryu,ynkjm/ryu,diogommartins/ryu,gopchandani/ryu,Tesi-Luca-Davide/ryu,habibiefaried/ryu,yamada-h/ryu,takahashiminoru/ryu,ynkjm/ryu,John-Lin/ryu,samrussell/ryu,yamt/ryu,gopchandani/ryu,zyq001/ryu,gareging/SDN_Framework,osrg/ryu,torufuru/oolhackathon,sivaramakrishnansr/ryu,castroflavio/ryu,zangree/ryu,ntts-clo/ryu,jazzmes/ryu,Tesi-Luca-Davide/ryu,alyosha1879/ryu,fkakuma/ryu,hisaharu/ryu,haniehrajabi/ryu,StephenKing/ryu,gareging/SDN_Framework,yamt/ryu,haniehrajabi/ryu,Tesi-Luca-Davide/ryu,iwaseyusuke/ryu,TakeshiTseng/ryu,osrg/ryu,StephenKing/summerschool-2015-ryu,lzppp/mylearning,zangree/ryu,hisaharu/ryu,jkoelker/ryu,umkcdcrg01/ryu_openflow,sivaramakrishnansr/ryu,zyq001/ryu,lsqtongxin/ryu,evanscottgray/ryu,OpenState-SDN/ryu,yamt/ryu,hisaharu/ryu,alyosha1879/ryu,elahejalalpour/ELRyu,diogommartins/ryu,ttsubo/ryu,ysywh/ryu,jazzmes/ryu,elahejalalpour/ELRyu,samrussell/ryu,shinpeimuraoka/ryu,alyosha1879/ryu,alanquillin/ryu,Zouyiran/ryu,mikhaelharswanto/ryu,ykaneko/ryu,diogommartins/ryu,shinpeimuraoka/ryu,Tesi-Luca-Davide/ryu,zangree/ryu,StephenKing/summerschool-2015-ryu,osrg/ryu,ykaneko/ryu,muzixing/ryu,evanscottgray/ryu,ttsubo/ryu,Tesi-Luca-Davide/ryu,yamt/ryu,darjus-amzn/ryu,fujita/ryu,sivaramakrishnansr/ryu,ysywh/ryu,darjus-amzn/ryu,Tejas-Subramanya/RYU_MEC,habibiefaried/ryu,openvapour/ryu,pichuang/ryu,Tejas-Subramanya/RYU_MEC,jalilm/ryu,torufuru/oolhackathon