MyFirstContribution: add avenues for getting help

With https://lore.kernel.org/git/20191114194708.GD60198@google.com/ we
now have a mentoring mailing list, to which we should direct new
contributors who have questions.

Mention #git-devel, which is targeted for Git contributors; asking for
help with getting a first contribution together is on-topic for that
channel. Also mention some of the conventions in case folks are
unfamiliar with IRC.

Because the mentoring list and #git-devel are both a subset of Git
contributors, finally list the main Git list and mention some of the
posting conventions.

Signed-off-by: Emily Shaffer <emilyshaffer@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/MyFirstContribution.txt

@@ -23,6 +23,39 @@ useful additional context:
 - `Documentation/SubmittingPatches`
 - `Documentation/howto/new-command.txt`
 
+[[getting-help]]
+=== Getting Help
+
+If you get stuck, you can seek help in the following places.
+
+==== https://groups.google.com/forum/#!forum/git-mentoring[git-mentoring@googlegroups.com]
+
+This mailing list is targeted to new contributors and is a great place to post
+questions and receive kind, detailed answers from volunteers on the Git
+project. You must join the group to view messages or post.
+
+==== https://webchat.freenode.net/#git-devel[#git-devel] on Freenode
+
+This IRC channel is for conversations between Git contributors. If someone is
+currently online and knows the answer to your question, you can receive help
+in real time. Otherwise, you can read the
+https://colabti.org/irclogger/irclogger_logs/git-devel[scrollback] to see
+whether someone answered you. IRC does not allow offline private messaging, so
+if you try to private message someone and then log out of IRC, they cannot
+respond to you. It's better to ask your questions in the channel so that you
+can be answered if you disconnect and so that others can learn from the
+conversation.
+
+==== git@vger.kernel.org
+
+This is the main Git project mailing list where code reviews, version
+announcements, design discussions, and more take place. The Git list
+requires plain-text-only emails and prefers inline and bottom-posting when
+replying to mail; you will be CC'd in all replies to you. Optionally, you can
+subscribe to the list by sending an email to majordomo@vger.kernel.org with
+"subscribe git" in the body. The https://lore.kernel.org/git[archive] of this
+mailing list is available to view in a browser.
+
 [[getting-started]]
 == Getting Started