Update PR template

Author: jianghao0718

.github/pull_request_template.md

@@ -1,3 +1,17 @@
+<!-- Welcome to backup-utils-private repo and Thanks for contributing!
+
+Note: Merging to the master branch will include your change in a future (unreleased) version of backup-utils. If the change needs to be shipped to the current release versions it will need to be backported. For more information, see the backport guide https://github.com/github/enterprise-releases/blob/master/docs/backport-an-existing-pr.md
+
+If you have any questions we can be found in the #ghes-backup-utils Slack channel.
+-->
+
+<!--
+Additional notes regarding CI:
+- All required CIs needs to be pass before merging PR
+- Integration test will run against enterprise2 repo with environment variable, do not re-run directly from janky or Github CI, please use Actions to re-run the failed tests
+- If you are making changes impacts cluster, please add `cluster` label or `[cluster]` in your PR title so it will trigger optional cluster integration test. Those tests will take about 3 hours so relax and come back later to check the results. ;)
+-->
+
 # PR Details
 
 ### Description