Remove outdated comment about extras not being supported.
Remove outdated comment about extras not being supported.

benesch/pip,jmagnusson/pip,alex/pip,pradyunsg/pip,squidsoup/pip,chaoallsome/pip,Gabriel439/pip,supriyantomaftuh/pip,qwcode/pip,sbidoul/pip,atdaemon/pip,fiber-space/pip,atdaemon/pip,blarghmatey/pip,pjdelport/pip,graingert/pip,willingc/pip,harrisonfeng/pip,cjerdonek/pip,squidsoup/pip,willingc/pip,jmagnusson/pip,prasaianooz/pip,ChristopherHogan/pip,mindw/pip,esc/pip,zenlambda/pip,qbdsoft/pip,alex/pip,patricklaw/pip,blarghmatey/pip,mujiansu/pip,atdaemon/pip,dstufft/pip,zvezdan/pip,graingert/pip,haridsv/pip,zvezdan/pip,pjdelport/pip,haridsv/pip,KarelJakubec/pip,natefoo/pip,ncoghlan/pip,RonnyPfannschmidt/pip,msabramo/pip,luzfcb/pip,ianw/pip,zorosteven/pip,supriyantomaftuh/pip,ncoghlan/pip,jamezpolley/pip,mujiansu/pip,esc/pip,rouge8/pip,yati-sagade/pip,benesch/pip,qwcode/pip,Carreau/pip,willingc/pip,natefoo/pip,graingert/pip,mattrobenolt/pip,harrisonfeng/pip,fiber-space/pip,pfmoore/pip,davidovich/pip,erikrose/pip,caosmo/pip,wkeyword/pip,haridsv/pip,xavfernandez/pip,dstufft/pip,nthall/pip,prasaianooz/pip,zenlambda/pip,ianw/pip,James-Firth/pip,rouge8/pip,msabramo/pip,alquerci/pip,RonnyPfannschmidt/pip,caosmo/pip,James-Firth/pip,chaoallsome/pip,jythontools/pip,qbdsoft/pip,tdsmith/pip,erikrose/pip,sigmavirus24/pip,minrk/pip,blarghmatey/pip,domenkozar/pip,radiosilence/pip,jasonkying/pip,davidovich/pip,KarelJakubec/pip,habnabit/pip,dstufft/pip,pfmoore/pip,tdsmith/pip,rbtcollins/pip,fiber-space/pip,mindw/pip,techtonik/pip,xavfernandez/pip,davidovich/pip,rbtcollins/pip,yati-sagade/pip,jythontools/pip,minrk/pip,caosmo/pip,pradyunsg/pip,luzfcb/pip,rouge8/pip,habnabit/pip,Gabriel439/pip,alquerci/pip,nthall/pip,squidsoup/pip,sbidoul/pip,techtonik/pip,ChristopherHogan/pip,RonnyPfannschmidt/pip,yati-sagade/pip,wkeyword/pip,sigmavirus24/pip,ChristopherHogan/pip,pypa/pip,alex/pip,nthall/pip,KarelJakubec/pip,techtonik/pip,h4ck3rm1k3/pip,mujiansu/pip,rbtcollins/pip,supriyantomaftuh/pip,zenlambda/pip,zorosteven/pip,pypa/pip,jamezpolley/pip,cjerdonek/pip,zorosteven/pip,luzfcb/pip,sigmavirus24/pip,Gabriel439/pip,ncoghlan/pip,mindw/pip,esc/pip,h4ck3rm1k3/pip,James-Firth/pip,benesch/pip,h4ck3rm1k3/pip,harrisonfeng/pip,natefoo/pip,Ivoz/pip,patricklaw/pip,xavfernandez/pip,erikrose/pip,zvezdan/pip,wkeyword/pip,qbdsoft/pip,pjdelport/pip,Carreau/pip,prasaianooz/pip,tdsmith/pip,Ivoz/pip,jasonkying/pip,jythontools/pip,mattrobenolt/pip,jamezpolley/pip,habnabit/pip,jasonkying/pip,jmagnusson/pip,chaoallsome/pip