docs: Add instructions for how to submit a merge request

[hans]

Good stuff!

docs/HowToReleaseLLVM.rst

266

Might as well make bugs.llvm.org a link I suppose?

267

s/$PROJ/llvm/ ?

Maybe expand the example a little in case people are confused about X and Y, e.g.

To request a patch to be merged to the branch for the 5.0.1 stable release, use this...

269

Link again, and maybe mention marking it as a blocker of the current release bug.. which I suppose one would have to search for, or know from the mailing list.

[tstellar]

Address review comments.

[hans]

Very nice, thanks!

docs/HowToReleaseLLVM.rst

 To help manage all the bugs reported and which ones are blockers or not, a new
 "[meta]" bug should be created and all regressions *blocking* that Meta. Once
 all blockers are done, the Meta can be closed.
 
 If a bug can't be reproduced, or stops being a blocker, it should be removed
 from the Meta and its priority decreased to *normal*. Debugging can continue,
 but on trunk.
 
+Merge Requests
+--------------
+
+You can use any of the following methods to request that a revision from trunk
+be merged into a release branch:
+
+#. Use the ``utils/release/merge-request.sh`` script which will automatically
+file a bug_ requesting that the patch be merged. e.g. To request revision
+12345 be merged into the branch for the 5.0.1 release:
+``llvm.src/utils/release/merge-request.sh -stable-version 5.0 -r 12345 -user [e-mail]``
+
+#. Manually file a bug_ with the subject: "Merge r12345 into the X.Y branch",
+enter the commit(s) that you want merged in the "Fixed by Commit(s)" and mark
+it as a blocker of the current release bug.  Release bugs are given aliases
+in the form of release-x.y.z, so to mark a bug as a blocker for the 5.0.1
+release, just enter release-5.0.1 in the "Blocks" field.
+
+#. Reply to the commit email on llvm-commits for the revision to merge and cc
+the release manager.
+
+.. _bug: https://bugs.llvm.org/
+
 Release Patch Rules
 -------------------
 
 Below are the rules regarding patching the release branch:
 
 #. Patches applied to the release branch may only be applied by the release
    manager, the official release testers or the code owners with approval from
    the release manager.