chore: add PR template (#1916)

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,42 @@
+<!--
+  - Thanks for submitting code to Blockly!  Please fill out the following as part of
+  - your pull request so we can review your code more easily.
+  -->
+
+## The basics
+
+<!-- TODO: Verify the following, checking each box with an 'x' between the brackets: [x] -->
+
+- [ ] I [validated my changes](https://developers.google.com/blockly/guides/contribute/samples#making_and_verifying_a_change)
+
+## The details
+### Resolves
+
+<!-- TODO: What Github issue does this resolve? Please include a link. -->
+Fixes 
+
+### Proposed Changes
+
+<!-- TODO: Describe what this Pull Request does.  Include screenshots if applicable. -->
+
+### Reason for Changes
+
+<!--TODO: Explain why these changes should be made.  Include screenshots if applicable. -->
+
+### Test Coverage
+
+<!-- TODO: Please create unit tests, and explain here how they cover
+           your changes, or tell us how you tested it manually. If
+           your changes include browser-specific behaviour, include
+           information about the browser and device that you used for
+           testing. -->
+
+### Documentation
+
+<!-- TODO: Does any documentation need to be created or updated because of this PR?
+  -        If so please explain.
+  -->
+
+### Additional Information
+
+<!-- Anything else we should know? -->