SubmittingPatches: clarify 'git-contacts' location

Use a dash ("git-contacts", not "git contacts") because the script is
not installed as part of "git" toolset. This also puts the script on
one line, which should make it easier to grep for with a loose search
query, such as

    $ git grep git.contacts Documentation

Also add a footnote to describe where the script is located, to help
readers who may not be familiar with such "contrib" scripts (and how
they are not accessible with the usual "git <subcommand>" syntax).

Signed-off-by: Linus Arver <linusa@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: Linus Arver

Documentation/SubmittingPatches

@@ -493,9 +493,13 @@ security relevant should not be submitted to the public mailing list
 mentioned below, but should instead be sent privately to the Git
 Security mailing list{security-ml-ref}.
 
+:contrib-scripts: footnoteref:[contrib-scripts,Scripts under `contrib/` are +
+not part of the core `git` binary and must be called directly. Clone the Git +
+codebase and run `perl contrib/contacts/git-contacts`.]
+
 Send your patch with "To:" set to the mailing list, with "cc:" listing
-people who are involved in the area you are touching (the `git
-contacts` command in `contrib/contacts/` can help to
+people who are involved in the area you are touching (the `git-contacts`
+script in `contrib/contacts/`{contrib-scripts} can help to
 identify them), to solicit comments and reviews.  Also, when you made
 trial merges of your topic to `next` and `seen`, you may have noticed
 work by others conflicting with your changes.  There is a good possibility