docs(pull_request_templates): Add Pull Request Template

.github/pull_request_template.md

@@ -0,0 +1,29 @@
+### Summary
+
+Provide a general description of the code changes in your pull
+request... were there any bugs you had fixed? If so, mention them like 'fixes #x'. If
+these bugs have open GitHub issues, be sure to tag them here as well,
+to keep the conversation linked together.
+
+### Other Information
+
+If there's anything else that's important and relevant to your pull
+request, mention that information here. This could include
+benchmarks, or other information.
+
+### Checklist
+
+Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes (`[x]`). This will ensure a smooth and quick review process.
+- [ ] I read the [Contributor Guide](./CONTRIBUTING.md) and followed the process outlined there for submitting PRs.
+
+<!--
+- [ ] My PR includes tests for *all* changed/updated/fixed behaviors (See [Test Coverage]).
+- [ ] All existing and new tests are passing.
+- [ ] I updated/added relevant documentation (doc comments with `///`).
+- [ ] The analyzer (`flutter analyze --flutter-repo`) does not report any problems on my PR.
+- [ ] I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement].
+- [ ] I signed the [CLA].
+- [ ] I am willing to follow-up on review comments in a timely manner.
+-->
+
+Thanks for contributing to coobjc!