Merge #1191

1191: Pull Request Template r=MikeInnes a=MikeInnes

Hopefully makes it a little clearer what the requirements are, which will lead to easier review, and encourage things like NEWS.md that we want to be better in sync.

cc @dhairyagandhi96 and @CarloLucibello for thoughts.

Co-authored-by: Mike J Innes <mike.j.innes@gmail.com>

.github/pull_request_template.md

@@ -0,0 +1,12 @@
+[Please delete this text and describe your change here.
+For bugfixes, please detail the bug and include a test case which your patch fixes.
+If you are adding a new feature, please clearly describe the design, its rationale, the possible alternatives considered.
+It is easiest to merge new features when there is clear precedent in other systems; we need to know we're taking
+the right direction since it can be hard to change later.]
+
+### PR Checklist
+
+- [ ] Tests are added
+- [ ] Entry in NEWS.md
+- [ ] Documentation, if applicable
+- [ ] Final review from `@MikeInnes` or `@dhairyagandhi96` (for API changes).