User-manual: "git stash <comment>" form is long gone

These days you must explicitly say "git stash save <comment>".

Signed-off-by: William Pursell <bill.pursell@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/user-manual.txt

@@ -1497,7 +1497,7 @@ so on a different branch and then coming back), unstash the
 work-in-progress changes.
 
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-$ git stash "work in progress for foo feature"
+$ git stash save "work in progress for foo feature"
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 This command will save your changes away to the `stash`, and