Documentation: "rebase <onto> <that>" stays on <that> branch upon exit

This change makes it clearer that the change to the history effected by
executing 'git rebase master' while on 'topic' branch, and by executing
'git rebase master topic' on any branch, will be the same; the implicit
checkout of the second form will remain after the rebase exits.
Signed-off-by: NDrew Northup <drew.northup@maine.edu>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-rebase.txt

@@ -66,8 +66,9 @@ would be:
     D---E---F---G master
 ------------
 
-The latter form is just a short-hand of `git checkout topic`
-followed by `git rebase master`.
+*NOTE:* The latter form is just a short-hand of `git checkout topic`
+followed by `git rebase master`. When rebase exits `topic` will
+remain the checked-out branch.
 
 If the upstream branch already contains a change you have made (e.g.,
 because you mailed a patch which was applied upstream), then that commit