Update README to point at a few key periodical messages to the list

They give a good starting point to new people who want to get
involved.  This owes suggestions by Martin Langhoff and Steven
Grimm.

Signed-off-by: Junio C Hamano <junkio@cox.net>

README

@@ -38,3 +38,9 @@ requests, comments and patches to git@vger.kernel.org. To subscribe
 to the list, send an email with just "subscribe git" in the body to
 majordomo@vger.kernel.org. The mailing list archives are available at
 http://marc.theaimsgroup.com/?l=git and other archival sites.
+
+The messages titled "A note from the maintainer", "What's in
+git.git (stable)" and "What's cooking in git.git (topics)" and
+the discussion following them on the mailing list give a good
+reference for project status, development direction and
+remaining tasks.