Add changelog entry for 3.6.0
Add changelog entry for 3.6.0

lmtierney/slack-irc,umegaya/slack-irc,erikdesjardins/slack-irc,php-ug/slack-irc,leeopop/slack-irc,andreaja/slack-irc,robertkety/slack-irc,ekmartin/slack-irc,reactiflux/discord-irc,chipx86/slack-irc,mxm/slack-irc