Documentation/merge-options.txt: describe -S/--gpg-sign for 'pull'

Pull has supported these since ea230d8 (pull: add the --gpg-sign
option, 2014-02-10).  Insert in long-option alphabetical order
following 7c85d274 (Documentation/merge-options.txt: order options
in alphabetical groups, 2009-10-22).

Signed-off-by: W. Trevor King <wking@tremily.us>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-merge.txt

@@ -64,12 +64,6 @@ OPTIONS
 -------
 include::merge-options.txt[]
 
--S[<keyid>]::
---gpg-sign[=<keyid>]::
-	GPG-sign the resulting merge commit. The `keyid` argument is
-	optional and defaults to the committer identity; if specified,
-	it must be stuck to the option without a space.
-
 -m <msg>::
 	Set the commit message to be used for the merge commit (in
 	case one is created).

Documentation/merge-options.txt

@@ -42,6 +42,12 @@ set to `no` at the beginning of them.
 	current `HEAD` is already up-to-date or the merge can be
 	resolved as a fast-forward.
 
+-S[<keyid>]::
+--gpg-sign[=<keyid>]::
+	GPG-sign the resulting merge commit. The `keyid` argument is
+	optional and defaults to the committer identity; if specified,
+	it must be stuck to the option without a space.
+
 --log[=<n>]::
 --no-log::
 	In addition to branch names, populate the log message with