DOC update PR checklist to be clearer

Author: beckermr

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,13 +1,12 @@
 <!--
-Thank you for pull request.
+Thank you for pull request!
+
 Please note that the `docs` subdir is generated from the sphinx sources in `src`, changes 
 to `.html` files will only be effective if applied to the respective `.rst`.
 -->
 
-<!--
-Please note any issues this fixes using [closing keywords]( https://help.github.com/articles/closing-issues-using-keywords/ ):
--->
+PR Checklist:
 
-<!--
-Please add any other relevant info below:
--->
+- [ ] make all edits to the docs in the `src` directory, not in `docs`
+- [ ] note any issues closed by this PR with [closing keywords](https://help.github.com/articles/closing-issues-using-keywords)
+- [ ] put any other relevant information below