chore: update pull request template

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,5 +1,7 @@
-Fixes #<issue_number_goes_here> (it's a good idea to open an issue first for discussion)
-
-- [ ] Tests and linter pass
+Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:
+- [ ] Make sure to open an issue as a [bug/issue](https://github.com/googleapis/{{metadata['repo']['name']}}/issues) before writing your code!  That way we can discuss the change, evaluate designs, and agree on the general idea
+- [ ] Ensure the tests and linter pass
 - [ ] Code coverage does not decrease (if any source code was changed)
 - [ ] Appropriate docs were updated (if necessary)
+
+Fixes #<issue_number_goes_here> 🦕