Document required base branch for pull requests.

Be explicit when submitting a PR about which branch to use as the base.

CONTRIBUTING.md

@@ -707,6 +707,8 @@ When submitting a Pull Request:
 
 - Write a detailed comment to describe the purpose of your submission and any issue(s), if any, it is resolving; a link to the GitHub issue is also helpful.
 
+- Select the `integration` branch as the base for your PR, do not select `main` nor any other branch.
+
 After submitting a Pull Request:
 
 - One or more reviewers will be assigned.

doc/xml/contributing.xml

@@ -816,6 +816,7 @@ pgbackrest/doc/doc.pl --out=html --include=user-guide --require=/quickstart --va
         <list>
             <list-item>Provide a short submission title.</list-item>
             <list-item>Write a detailed comment to describe the purpose of your submission and any issue(s), if any, it is resolving; a link to the GitHub issue is also helpful.</list-item>
+            <list-item>Select the <code>integration</code> branch as the base for your PR, do not select <code>main</code> nor any other branch.</list-item>
         </list>
 
         <p>After submitting a Pull Request:</p>

doc/xml/release.xml

@@ -391,6 +391,17 @@
 
                         <p>Simplify messaging around supported versions in the documentation.</p>
                     </release-item>
+
+                    <release-item>
+                        <github-pull-request id="1722"/>
+
+                        <release-item-contributor-list>
+                            <release-item-contributor id="david.christensen"/>
+                            <release-item-reviewer id="reid.thompson"/>
+                        </release-item-contributor-list>
+
+                        <p>Document required base branch for pull requests.</p>
+                    </release-item>
                 </release-improvement-list>
             </release-doc-list>
         </release>