Doc branch: show -vv option and alternative

Indicate that the -v option can be given twice in the short options.
Without it users pass over the option. Also indicate the alternate
'git remote show' method.

Signed-off-by: Philip Oakley <philipoakley@iee.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-branch.txt

@@ -129,11 +129,13 @@ This option is only applicable in non-verbose mode.
 	use `git branch --list <pattern>` to list matching branches.
 
 -v::
+-vv::
 --verbose::
 	When in list mode,
 	show sha1 and commit subject line for each head, along with
 	relationship to upstream branch (if any). If given twice, print
-	the name of the upstream branch, as well.
+	the name of the upstream branch, as well (see also `git remote
+	show <remote>`).
 
 -q::
 --quiet::