Update information about Python 3
Update information about Python 3

Python 3 and Flask is a good combination nowadays that works rather well. In fact, [most PyPI libs](https://regebro.wordpress.com/2014/10/23/59-of-maintained-packages-support-python-3/) are now ported and it's generally ok to encourage people to use Python 3 for new projects.
postelin/flask,ankravch/flask,jstacoder/flask,fevxie/flask,SsangYoon/Flask,RohithKP/flask,tcnoviembre2013/flask,wtorcasoGB/flask,nwags/flask,AndreaEdwards/flask,xujianhai/flask,stephaniemertz/flask,fkazimierczak/flask,qinfengsuiyu/flask,ezequielo/flask,sonnyhu/flask,tangfeng1/flask,SsangYoon/Flask,antsar/flask,suppandi/flask,s7v7nislands/flask,wilbert-abreu/flask,robertglen/flask,mitsuhiko/flask,niima/flask,rawrgulmuffins/flask,pallets/flask,lord63-forks/flask,jorpramo/flask,Papa2k15/flask,ankurpandey/flask,onetinyr/flask,artleaf/flask,jenalgit/flask,gaomingnudt/gm-flask2.0,lyn233/flask,flamelizard/flask,ZacariasBendeck/flask,iamantee/flask,moluzhang/flask,nju520/flask,garaden/flask,Freebird2014/flask,auready/flask,dominjune/flask,dominjune/flask,auready/flask,godfreyy/flask,RohithKP/flask,JingZhou0404/flask,AvivC/flask,adrianmoisey/cptdevops,wangjun/flask,huwenhui/flask,gangeshwark/flask,chenke91/flask,sixpi/flask,tristanfisher/flask,Endika/flask,elelianghh/flask,wilbert-abreu/flask,tripathi62674/flask,liuyi1112/flask,zailushangde/flask,XGiton/flask,kuku940/flask,rollingstone/flask,ZacariasBendeck/flask,bodefuwa/flask,godfreyy/flask,karen-wang/flask,justanr/flask,gangeshwark/flask,raven47git/flask,HeyItsAlan/flask,AvivC/flask,wangjun/flask,xiaoshaozi52/flask,jonieli/flask,Freebird2014/flask,artleaf/flask,algoStruct/flask,wtl-zju/flask,fkazimierczak/flask,ghhong1986/flask,drewja/flask,jonieli/flask,oculardexterity/flask,pxzhenren/flask,mAzurkovic/flask,liuyi1112/flask,TylerB24890/flask,qinfengsuiyu/flask,nju520/flask,suppandi/flask,flamelizard/flask,Parkayun/flask,oculardexterity/flask,visaxin/flask,karen-wang/flask,vivekanand1101/flask,VShangxiao/flask,kyle-sorensen/flask,margguo/flask,s7v7nislands/flask,cheesecake4392/flask,lynget/flask,kyle-sorensen/flask,kuhli/flask,gaomingnudt/gm-flask2.0,pallets/flask,Eagles2F/flask,alexwidener/flask,jawed123/flask,ezequielo/flask,postelin/flask,tangfeng1/flask,ezequielo/flask,Ricardo666666/flask,gbolahanalade/flask,wudafucode/flask,hoatle/flask,liaoqingwei/flask,TylerB24890/flask,nZac/flask,dhruvsrivastava/flask,horica-ionescu/flask,WSDC-NITWarangal/flask,abdulbaqi/flask,brianbeale/flask,wudafucode/flask,JingZhou0404/flask,tony/flask,margguo/flask,AndreaEdwards/flask,cgvarela/flask,skmezanul/flask,ankurpandey/flask,rawrgulmuffins/flask,edcomstock/flask,Parkayun/flask,ryandvill/flask,vishnugonela/flask,wldtyp/flask,homeworkprod/flask,gbolahanalade/flask,GavinCruise/flask,jenalgit/flask,happyspace/flask,pxzhenren/flask,dawran6/flask,HeyItsAlan/flask,GavinCruise/flask,grayswand1r/flask,bluedazzle/flask,fanshaohua-fan/flask,algoStruct/flask,Papa2k15/flask,beni55/flask,mysweet/flask,sam-tsai/flask,EasonYi/flask,tony/flask,lyn233/flask,JamesTFarrington/flask,chenke91/flask,kyle-sorensen/flask,zoyanhui/flask,mujiatong/flask,adrianmoisey/cptdevops,sonnyhu/flask,jorpramo/flask,horica-ionescu/flask,felipefuka/flask,liukaijv/flask,justanr/flask,jonatanblue/flask,vivekanand1101/flask,AndreaEdwards/flask,visaxin/flask,hyunchel/flask,sixpi/flask,ABaldwinHunter/flask-clone-classic,gilesburnfield/flask,tjxiter/flask,ffsdmad/flask,warm200/flask,theo-l/flask,arvinls/flask,fengsp/flask,pallets/flask,Ricardo666666/flask,theo-l/flask,karlw00t/flask,raven47git/flask,tristanfisher/flask,Faiz7412/flask,mitchfriedman/flask,anujk3/flask,aniketshukla/flask,hyunchel/flask,EasonYi/flask,mysweet/flask,elelianghh/flask,drewja/flask,tripathi62674/flask,fanshaohua-fan/flask,wtl-zju/flask,XGiton/flask,liuyi1112/flask,Eagles2F/flask,nwags/flask,nZac/flask,suppandi/flask,flabe81/flask,s7v7nislands/flask,sage417/flask,liaoqingwei/flask,artleaf/flask,tjxiter/flask,blankme/flask,huwenhui/flask,lynget/flask,mujiatong/flask,VShangxiao/flask,sam-tsai/flask,bodefuwa/flask,vishnugonela/flask,chenrenyi/flask,szymonm/flask,fengsp/flask,cliu-aa/flask,godfreyy/flask,tcnoviembre2013/flask,jonatanblue/flask,VShangxiao/flask,ryandvill/flask,q1ang/flask,nju520/flask,jenalgit/flask,cheesecake4392/flask,algoStruct/flask,karlw00t/flask,gangeshwark/flask,szymonm/flask,luzzyzhang/flask,warm200/flask,jstacoder/flask,jiimaho/flask,homeworkprod/flask,hoatle/flask,aniketshukla/flask,EasonYi/flask,garaden/flask,zailushangde/flask,arvinls/flask,chenke91/flask,TylerB24890/flask,bluedazzle/flask,luvten/flask,chuijiaolianying/flask,visaxin/flask,xujianhai/flask,treedledee/flask,tangfeng1/flask,pledo/flask,happyspace/flask,jonieli/flask,ghhong1986/flask,chuijiaolianying/flask,luzzyzhang/flask,ankurpandey/flask,kuhli/flask,cgvarela/flask,LonglyCode/flask,oculardexterity/flask,grayswand1r/flask,dawran6/flask,ankravch/flask,brianbeale/flask,karen-wang/flask,lord63-forks/flask,Ricardo666666/flask,wldtyp/flask,dhruvsrivastava/flask,robertglen/flask,anujk3/flask,luvten/flask,beni55/flask,niima/flask,onetinyr/flask,ffsdmad/flask,szymonm/flask,wtorcasoGB/flask,felipefuka/flask,lalinsky/flask,mitchfriedman/flask,xiaoshaozi52/flask,fevxie/flask,pinkpet/flask,onetinyr/flask,WSDC-NITWarangal/flask,warm200/flask,Faiz7412/flask,LonglyCode/flask,jeezybrick/flask,chenrenyi/flask,stephaniemertz/flask,cliu-aa/flask,chuijiaolianying/flask,anujk3/flask,jeezybrick/flask,justanr/flask,alanhamlett/flask,liukaijv/flask,pinkpet/flask,zoyanhui/flask,fkazimierczak/flask,postelin/flask,liaoqingwei/flask,lalinsky/flask,Faiz7412/flask,ryandvill/flask,pledo/flask,jstacoder/flask,gilesburnfield/flask,abdulbaqi/flask,DesQi/flask,drewja/flask,SsangYoon/Flask,ABaldwinHunter/flask-clone-classic,edcomstock/flask,treedledee/flask,alexwidener/flask,flabe81/flask,q1ang/flask,rollingstone/flask,JamesTFarrington/flask,raven47git/flask,skmezanul/flask,mAzurkovic/flask,mitsuhiko/flask,antsar/flask,jorpramo/flask,GavinCruise/flask,DesQi/flask,sage417/flask,Endika/flask,iamantee/flask,jawed123/flask,kuku940/flask,blankme/flask,happyspace/flask,vishnugonela/flask,moluzhang/flask,alanhamlett/flask,alanhamlett/flask,jiimaho/flask