Documentation: -stable rules: upstream commit ID requirement reworded

It is a hard requirement to include the upstream commit ID in the
changelog of a -stable submission, not just a courtesy to the stable
team. This concerns only mail submission though, which is no longer
the only way into stable. (Also, fix a double "the".)

Signed-off-by: Stefan Richter <[e-mail]>
Acked-by: Randy Dunlap <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/stable_kernel_rules.txt

···
  - It cannot contain any "trivial" fixes in it (spelling changes,
    whitespace cleanups, etc).
  - It must follow the Documentation/SubmittingPatches rules.
- - It or an equivalent fix must already exist in Linus' tree.  Quote the
-   respective commit ID in Linus' tree in your patch submission to -stable.
+ - It or an equivalent fix must already exist in Linus' tree (upstream).
 
 
 Procedure for submitting patches to the -stable tree:
 
  - Send the patch, after verifying that it follows the above rules, to
-   [e-mail].
- - To have the patch automatically included in the stable tree, add the
-   the tag
+   [e-mail].  You must note the upstream commit ID in the changelog
+   of your submission.
+ - To have the patch automatically included in the stable tree, add the tag
      Cc: [e-mail]
    in the sign-off area. Once the patch is merged it will be applied to
    the stable tree without anything else needing to be done by the author