Merge branch 'hv/doc-commit-reference-style'

A small doc update.

* hv/doc-commit-reference-style:
  SubmittingPatches: document how to reference previous commits

Documentation/SubmittingPatches

@@ -121,6 +121,11 @@ its behaviour.  Try to make sure your explanation can be understood
 without external resources. Instead of giving a URL to a mailing list
 archive, summarize the relevant points of the discussion.
 
+If you want to reference a previous commit in the history of a stable
+branch use the format "abbreviated sha1 (subject, date)". So for example
+like this: "Commit f86a374 (pack-bitmap.c: fix a memleak, 2015-03-30)
+noticed [...]".
+
 
 (3) Generate your patch using Git tools out of your commits.