Add change checklist to PR template, including item to post change announcement per (NREL#106

Author: softwareengineerprogrammer

.github/pull_request_template.md

@@ -11,4 +11,21 @@ and any other relevant information.
 
 ---
 
-*Additional metadata such as TODO items or link to self-reviews (PR into your own fork created prior to submission)*
+**Change Checklist**:
+
+Before merging:
+1. [ ] Add a CHANGELOG entry ([example](https://github.com/NREL/GEOPHIRES-X/commit/15e10e5c3c08633a16645e41dfb7e8131805483f)). RST Template:
+```restructuredtext
+M.m.P: `TITLE <https://github.com/NREL/GEOPHIRES-X/pull/PR-NUMBER>`__ | `release <https://github.com/NREL/GEOPHIRES-X/releases/tag/vM.m.P>`__
+```
+
+After merging:
+1. [ ] Push tag(s) to GitHub: `git push origin refs/tags/vM.m.P`
+1. [ ] Post a change announcement to the [GEOPHIRES Change Announcements Discussion](https://github.com/NREL/GEOPHIRES-X/discussions/428) ([example](https://github.com/NREL/GEOPHIRES-X/discussions/428#discussioncomment-14593405)). Markdown template:
+```markdown
+M.m.p: [TITLE](https://github.com/NREL/GEOPHIRES-X/pull/PR-NUMBER) | [release](https://github.com/NREL/GEOPHIRES-X/releases/tag/vM.m.P)`
+```
+
+---
+
+*Additional metadata such as TODO items or link to your initial self-review (PR into your own fork created prior to submission)*