feat: add pull request template

Author: kayjan

.github/pull_request_template.md

@@ -0,0 +1,14 @@
+## Description
+<!-- Provide a concise description of changes and the reason for the change -->
+
+## Testing
+<!-- Describe the tests added (tests for new feature, tests for bugfix) -->
+
+## Additional notes
+<!-- Any information that might be useful for review -->
+
+## Checklist
+I have read through the [contributing guidelines](https://bigtree.readthedocs.io/en/stable/home/contributing/) and ensured that
+- [ ] I have followed the convention and standards, and my code is checked for style and correctness.
+- [ ] I have added test cases and ensured unit tests passed and code coverage is 100%.
+- [ ] I have ensured documentation and code docstrings are up-to-date.