README: change http links to https
README: change http links to https

Also fix one instance of uncapitalized "kakoune"
Somasis/kakoune,mawww/kakoune,casimir/kakoune,Somasis/kakoune,danr/kakoune,Somasis/kakoune,alexherbo2/kakoune,casimir/kakoune,Somasis/kakoune,alexherbo2/kakoune,casimir/kakoune,occivink/kakoune,jkonecny12/kakoune,occivink/kakoune,casimir/kakoune,jkonecny12/kakoune,mawww/kakoune,occivink/kakoune,mawww/kakoune,lenormf/kakoune,lenormf/kakoune,mawww/kakoune,danr/kakoune,lenormf/kakoune,alexherbo2/kakoune,jkonecny12/kakoune,jkonecny12/kakoune,danr/kakoune,alexherbo2/kakoune,danr/kakoune,occivink/kakoune,lenormf/kakoune