Update docs to describe new PR release-note block parsing.

docs/devel/cherry-picks.md

@@ -50,9 +50,12 @@ label changes to the **master** branch PR:
   * Add an appropriate release-note-(!label-needed) label
   * Add an appropriate milestone
   * Add the `cherrypick-candidate` label
-  * The PR title is the **release note** you want published at release time and
-note that PR titles are mutable and should reflect a release note
-friendly message for any `release-note-*` labeled PRs.
+1. `release-note` labeled PRs generate a release note using the PR title by
+   default OR the release-note block in the PR template if filled in.
+  * See the [PR template](../../.github/PULL_REQUEST_TEMPLATE.md) for more
+    details.
+  * PR titles and body comments are mutable and can be modified at any time
+    prior to the release to reflect a release note friendly message.
 
 ### How do cherrypick-candidates make it to the release branch?
 

docs/devel/pull-requests.md

@@ -75,14 +75,18 @@ The following will save time for both you and your reviewer:
 ## Release Notes
 
 This section applies only to pull requests on the master branch.
+For cherry-pick PRs, see the [Cherrypick instructions](cherry-picks.md)
 
 1. All pull requests are initiated with a `release-note-label-needed` label.
 1. For a PR to be ready to merge, the `release-note-label-needed` label must be removed and one of the other `release-note-*` labels must be added.
 1. `release-note-none` is a valid option if the PR does not need to be mentioned
  at release time.
-1. The PR title is the **release note** you want published at release time.
-  * NOTE: PR titles are mutable and should reflect a release note friendly
-    message for any `release-note-*` labeled PRs.
+1. `release-note` labeled PRs generate a release note using the PR title by
+   default OR the release-note block in the PR template if filled in.
+  * See the [PR template](../../.github/PULL_REQUEST_TEMPLATE.md) for more
+    details.
+  * PR titles and body comments are mutable and can be modified at any time
+    prior to the release to reflect a release note friendly message.
 
 The only exception to these rules is when a PR is not a cherry-pick and is
 targeted directly to the non-master branch.  In this case, a `release-note-*`