ANDROID: README: Add requirement for "Bug:" tag for FROMLIST

There needs to be a bug for FROMLIST patches to discuss
rationale for why the patch is so urgent that it needs
to be merged before maintainers accept it upstream.

Bug: 155420414
Signed-off-by: Todd Kjos <tkjos@google.com>
Change-Id: I33bfc9b1edcead7a9b300ba57a2d371a9ea2f74e

README.md

@@ -111,6 +111,8 @@ must be a stable maintainer branch (not rebased, so don't use `linux-next` for e
 - If the patch has been submitted to LKML, but not accepted into any maintainer tree
     - tag the patch subject with `FROMLIST:`
     - add a `Link:` tag with a link to the submittal on lore.kernel.org
+    - add a `Bug:` tag with the Android bug (required for patches not accepted into
+a maintainer tree)
     - if changes were required, use `BACKPORT: FROMLIST:`
     - Example:
 ```