Update PULL_REQUEST_TEMPLATE.md

Author: pcihon

.github/PULL_REQUEST_TEMPLATE.md

@@ -25,3 +25,5 @@ Thanks again!
 - [ ] I have reviewed my changes in staging. (look for the **deploy-to-heroku** link in your pull request, then click **View deployment**)
 - [ ] For content changes, I have reviewed the [localization checklist](https://github.com/github/docs/blob/main/contributing/localization-checklist.md)
 - [ ] For content changes, I have reviewed the [Content style guide for GitHub Docs](https://github.com/github/docs/blob/main/contributing/content-style-guide.md).
+
+### Public summary for site-policy changes: