doc: Add an IRC badge linking to Freenode
doc: Add an IRC badge linking to Freenode

Fixes #1266

alexherbo2/kakoune,Somasis/kakoune,jjthrash/kakoune,casimir/kakoune,jkonecny12/kakoune,occivink/kakoune,lenormf/kakoune,danr/kakoune,Somasis/kakoune,jjthrash/kakoune,mawww/kakoune,jjthrash/kakoune,casimir/kakoune,occivink/kakoune,jjthrash/kakoune,Somasis/kakoune,jkonecny12/kakoune,jkonecny12/kakoune,occivink/kakoune,alexherbo2/kakoune,alexherbo2/kakoune,danr/kakoune,mawww/kakoune,jkonecny12/kakoune,mawww/kakoune,Somasis/kakoune,alexherbo2/kakoune,danr/kakoune,mawww/kakoune,casimir/kakoune,danr/kakoune,lenormf/kakoune,occivink/kakoune,lenormf/kakoune,casimir/kakoune,lenormf/kakoune