Add Discord server to README

Author: essen

README.asciidoc

@@ -38,6 +38,6 @@ and https://pleroma.social/[Pleroma].
 
 == Getting help
 
-* Official IRC Channel: #ninenines on irc.freenode.net
+* https://discord.gg/x468ZsxG[Discord server]
 * https://github.com/ninenines/gun/issues[Issues tracker]
 * https://ninenines.eu/services/[Commercial Support]