Documentation cherry-pick: Fix cut-and-paste error

Signed-off-by: Mike Ralphson <mike@abacus.co.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-cherry-pick.txt

@@ -45,7 +45,7 @@ OPTIONS
 	default is not to do `-x` so this option is a no-op.
 
 -m parent-number|--mainline parent-number::
-	Usually you cannot revert a merge because you do not know which
+	Usually you cannot cherry-pick a merge because you do not know which
 	side of the merge should be considered the mainline.  This
 	option specifies the parent number (starting from 1) of
 	the mainline and allows cherry-pick to replay the change