MNT: add pull request template (#2443)

So we don't have to request changes on these basic requirements as
often - hopefully :)

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,36 @@
+<!-- Hello! Thanks for submitting a PR. To help make things go a bit more
+     smoothly we would appreciate that you go through this template. -->
+
+### Description
+
+<!-- Good things to put here include: reasoning for the change (please link
+     any relevant issues!), any noteworthy (or hacky) choices to be aware of,
+     or what the problem resolved here looked like ... we won't mind a ranty
+     story :) -->
+
+### Checklist - did you ...
+
+<!-- If any of the following items aren't relevant for your contribution
+     please still tick them so we know you've gone through the checklist.
+
+    All user-facing changes should get an entry. Otherwise, signal to us
+    this should get the magical label to silence the CHANGELOG entry check.
+    Tests are required for bugfixes and new features. Documentation changes
+    are necessary for formatting and most enhancement changes. -->
+
+- [] Add a CHANGELOG entry if necessary?
+- [] Add / update tests if necessary?
+- [] Add new / update outdated documentation?
+
+<!-- Just as a reminder, everyone in all psf/black spaces including PRs
+     must follow the PSF Code of Conduct (link below).
+
+     Finally, once again thanks for your time and effort. If you have any
+     feedback in regards to your experience contributing here, please
+     let us know!
+
+     Helpful links:
+
+      PSF COC: https://www.python.org/psf/conduct/
+      Contributing docs: https://black.readthedocs.io/en/latest/contributing/index.html
+      Chat on Python Discord: https://discord.gg/RtVdv86PrH -->