General: add PR template

This should help folks craft Pull Request descriptions that are as helpful as they can be.

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,22 @@
+<!--- Provide a general summary of your changes in the Title above -->
+
+Fixes #
+
+## Proposed changes:
+<!--- Explain what functional changes your PR includes -->
+*
+
+### Other information:
+
+- [ ] Have you written new tests for your changes, if applicable?
+
+## Testing instructions:
+<!-- If you were reviewing this PR, how would you like the instructions to be presented? -->
+<!-- Please include detailed testing steps, explaining how to test your change. -->
+<!-- Bear in mind that context you working on is not obvious for everyone.  -->
+<!-- Adding "simple" configuration steps will help reviewers to get to your PR as quickly as possible. -->
+<!-- "Before / After" screenshots can also be very helpful when the change is visual. -->
+
+* Go to '..'
+*
+