Add supported ruby versions to readme
Add supported ruby versions to readme

coinbase/modified-doorkeeper,doorkeeper-gem/doorkeeper,identification-io/doorkeeper,CloudTags/doorkeeper,vanboom/doorkeeper,outstand/doorkeeper,moneytree/doorkeeper,CloudTags/doorkeeper,AdStage/doorkeeper,jasl/doorkeeper,ngpestelos/doorkeeper,telekomatrix/doorkeeper,EasterAndJay/doorkeeper,ezilocchi/doorkeeper,daande/doorkeeper,Tout/doorkeeper,GeekOnCoffee/doorkeeper,kolorahl/doorkeeper,AdStage/doorkeeper,AICIDNN/doorkeeper,stefania11/doorkeeper,coinbase/modified-doorkeeper,ministryofjustice/doorkeeper,ValMilkevich/doorkeeper,lalithr95/doorkeeper,Tout/doorkeeper,jasl/doorkeeper,nbulaj/doorkeeper,ifeelgoods/doorkeeper,jasl/doorkeeper,ngpestelos/doorkeeper,ministryofjustice/doorkeeper,ifeelgoods/doorkeeper,pmdeazeta/doorkeeper,Tout/doorkeeper,shivakumaarmgs/doorkeeper,stormz/doorkeeper,6fusion/doorkeeper,doorkeeper-gem/doorkeeper,AICIDNN/doorkeeper,outstand/doorkeeper,calfzhou/doorkeeper,ValMilkevich/doorkeeper,phillbaker/doorkeeper,coinbase/modified-doorkeeper,doorkeeper-gem/doorkeeper,stormz/doorkeeper,vovimayhem/doorkeeper,Uysim/doorkeeper,mavenlink/doorkeeper,outstand/doorkeeper,dollarshaveclub/doorkeeper,kolorahl/doorkeeper,vanboom/doorkeeper,CloudTags/doorkeeper,mavenlink/doorkeeper,pmdeazeta/doorkeeper,identification-io/doorkeeper,GeekOnCoffee/doorkeeper,EasterAndJay/doorkeeper,CloudTags/doorkeeper,lalithr95/doorkeeper,stefania11/doorkeeper,nbulaj/doorkeeper,vovimayhem/doorkeeper,telekomatrix/doorkeeper,dk1234567/doorkeeper,ukasiu/doorkeeper,shivakumaarmgs/doorkeeper,mavenlink/doorkeeper,6fusion/doorkeeper,dk1234567/doorkeeper,ukasiu/doorkeeper,dollarshaveclub/doorkeeper,calfzhou/doorkeeper,ezilocchi/doorkeeper,moneytree/doorkeeper,daande/doorkeeper,Uysim/doorkeeper,ifeelgoods/doorkeeper