Create PULL_REQUEST_TEMPLATE.md (#14)

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,12 @@
+Fixes #
+Design discussion issue (if applicable) #
+
+## Changes
+
+Please provide a brief description of the changes here.
+
+## Merge requirement checklist
+
+* [ ] [CONTRIBUTING](https://github.com/NillionNetwork/nada-dsl/blob/main/CONTRIBUTING.md) guidelines followed
+* [ ] Unit tests added/updated (if applicable)
+* [ ] Backwards compatability analysis completed (if applicable). "Will this change require recompilation and upload of user programs?"