Add a pull request template

.github/PULL_REQUEST_TEMPLATE

@@ -0,0 +1,21 @@
+
+### PR guidelines
+
+- Everything needs to be tested. This can be done with or without QA as appropriate. When in doubt, _ask_.
+- Skim over your diff at least once before submitting. By skimming over the diff, you may catch glaring errors, merge issues, etc. that may otherwise waste time in code review.
+
+Fill out the form below (replace the space between the brackets with an `x` if the statement is accurate). The provided release notes will appear in #pc-release.
+
+(You may delete the following divider and everything above it)
+
+---
+
+- [ ] I have tested, to the best of my ability, the changes being submitted.
+
+Public release notes:
+- One
+- Two
+- Threeee
+
+Internal / private release notes (if applicable):
+- Four