Document "git stash message..."
Document "git stash message..."

The command was recently updated to take message on the command line, but
this feature has not been documented.

Signed-off-by: Nanako Shiraishi <7d97fbf70141dda63063292abadb698cc511a125@bluebottle.com>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git