in Contribute, say IRC server is Freenode

Someone wanted this information two years ago on https://github.com/kschiess/parslet/issues/12 , and today I, too, wanted this information.

I’m not an expert at IRC, so if calling the server “Freenode” is better than “irc.freenode.net” because everybody knows Freenode’s address, feel free to change that.