Hacking-Git: add Discord and maintainer's note

Author: chriscool

Diff for: Hacking-Git.md

@@ -126,8 +126,12 @@ suggest improvements. Thanks!
 
 * [#git-devel IRC channel archive](https://colabti.org/irclogger/irclogger_logs/git-devel)
 
+* [Git Community Discord Server](https://discord.gg/NKY7fFue)
+
 * [git-mentoring mailing list](https://groups.google.com/forum/#!forum/git-mentoring)
 
+* ["A note from the maintainer"](https://github.com/git/git/blob/todo/MaintNotes)
+
 ## Mentoring programs
 
 * [Google Summer of Code](https://summerofcode.withgoogle.com/)