SubmittingPatches: add heading for format-patch and send-email

Signed-off-by: Linus Arver <linusa@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: Linus Arver

Documentation/SubmittingPatches

@@ -430,6 +430,8 @@ Do not forget to add trailers such as `Acked-by:`, `Reviewed-by:` and
 `Tested-by:` lines as necessary to credit people who helped your
 patch, and "cc:" them when sending such a final version for inclusion.
 
+==== `format-patch` and `send-email`
+
 Learn to use `format-patch` and `send-email` if possible.  These commands
 are optimized for the workflow of sending patches, avoiding many ways
 your existing e-mail client (often optimized for "multipart/*" MIME