chore: add PR template (#76)

* chore: add PR template

Closes ENG-1818

* chore: simplify PR template

Author: init4samwise

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,12 @@
+## Description
+
+<!-- Brief description of changes -->
+
+## Related Issue
+
+<!-- Link to Linear issue: Closes ENG-XXX -->
+
+## Testing
+
+- [ ] Tests pass locally
+- [ ] New tests added (if applicable)