SubmittingPatches: mention the git contacts command

Instead of just mentioning 'git blame' and 'git shortlog', which make it
quite hard for new contributors to pick out the appropriate list of
people to cc on their patch series, mention the 'git contacts' utility,
which makes it much easier to get a reasonable list of contacts for a
change.

This should help new contributors pick out a reasonable cc list by
simply using a single command.

Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/SubmittingPatches

@@ -260,8 +260,8 @@ that starts with `-----BEGIN PGP SIGNED MESSAGE-----`.  That is
 not a text/plain, it's something else.
 
 Send your patch with "To:" set to the mailing list, with "cc:" listing
-people who are involved in the area you are touching (the output from
-`git blame $path` and `git shortlog --no-merges $path` would help to
+people who are involved in the area you are touching (the `git
+contacts` command in `contrib/contacts/` can help to
 identify them), to solicit comments and reviews.
 
 :1: footnote:[The current maintainer: gitster@pobox.com]