cat-file: mention --unordered along with --batch-all-objects

The note on ordering for --batch-all-objects was written when that was
the only possible ordering. These days we have --unordered, too, so
let's point to it.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-cat-file.txt

@@ -94,8 +94,9 @@ OPTIONS
 	Instead of reading a list of objects on stdin, perform the
 	requested batch operation on all objects in the repository and
 	any alternate object stores (not just reachable objects).
-	Requires `--batch` or `--batch-check` be specified. Note that
-	the objects are visited in order sorted by their hashes.
+	Requires `--batch` or `--batch-check` be specified. By default,
+	the objects are visited in order sorted by their hashes; see
+	also `--unordered` below.
 
 --buffer::
 	Normally batch output is flushed after each object is output, so