Mention updating the unreleased changelog section (#1935)

* Initial plan

* Update CONTRIBUTING.md to mention updating Unreleased changelog section

Co-authored-by: Goooler <10363352+Goooler@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Goooler <10363352+Goooler@users.noreply.github.com>

Author: Copilot

CONTRIBUTING.md

@@ -69,4 +69,5 @@ When adding new features or public APIs:
 5. Run `./gradlew lint` to check for potential issues
 6. Optionally, run `./gradlew build` to run compilation, tests, and standard verification tasks configured for the project
 7. Ensure your commit messages are clear and descriptive
+8. Update the `Unreleased` section in [CHANGELOG](docs/changes/README.md) if applicable