add the note for catkin_prepare_release. (backport #5713)

source/How-To-Guides/Releasing/_Bump-Package-Version.rst

@@ -1,4 +1,5 @@
 Every release of the package must have a unique version number higher than the previous release.
+
 Run:
 
 .. code-block:: console
@@ -18,3 +19,9 @@ which performs the following:
    By default the patch version of the package is incremented, such as from ``0.0.0`` to ``0.0.1``.
    To increment the minor or major version instead, run ``catkin_prepare_release --bump minor`` or ``catkin_prepare_release --bump major``.
    For more details, see ``catkin_prepare_release --help``.
+
+.. note::
+
+   If your repository has a strict merge rule like ``Require a pull request before merging``, you will need to create a pull request with the changes/tag generated by ``catkin_prepare_release`` and then merge that, since you cannot directly push to the branch.
+   Depending on your repository's pull request merge settings (such as squash merge or rebase merge), merging the pull request may change the SHA of the version commit.
+   In such cases, you will need to manually re-tag the version commit after merging to ensure the tag points to the correct commit.