ci: Update PR template to clarify conventional commit syntax

Author: holtskinner

.github/PULL_REQUEST_TEMPLATE.md

@@ -5,6 +5,9 @@ Before submitting your PR, there are a few things you can do to make sure it goe
 
 - [ ] Follow the [`CONTRIBUTING` Guide](https://github.com/google-a2a/a2a-python/blob/main/CONTRIBUTING.md).
 - [ ] Make your Pull Request title in the <https://www.conventionalcommits.org/> specification.
+  - `fix:` which represents bug fixes, and correlates to a [SemVer](https://semver.org/) patch.
+  - `feat:` represents a new feature, and correlates to a SemVer minor.
+  - `feat!:`, or `fix!:`, `refactor!:`, etc., which represent a breaking change (indicated by the `!`) and will result in a SemVer major.
 - [ ] Ensure the tests and linter pass (Run `nox -s format` from the repository root to format)
 - [ ] Appropriate docs were updated (if necessary)