Documentation: branch.*.merge can also affect 'git-push'

Signed-off-by: Santi Béjar <santi@agolina.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -480,7 +480,7 @@ branch.<name>.remote::
 branch.<name>.merge::
 	Defines, together with branch.<name>.remote, the upstream branch
 	for the given branch. It tells 'git-fetch'/'git-pull' which
-	branch to merge from.
+	branch to merge and can also affect 'git-push' (see push.default).
 	When in branch <name>, it tells 'git-fetch' the default
 	refspec to be marked for merging in FETCH_HEAD. The value is
 	handled like the remote part of a refspec, and must match a