docs: add Contributing section to README

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Patel230

README.md

@@ -66,6 +66,10 @@ with HawkClient() as client:
 
 See the [examples/](examples/) directory for complete runnable examples.
 
+## Contributing
+
+Contributions are welcome — please read [CONTRIBUTING.md](CONTRIBUTING.md) before opening a pull request.
+
 ## License
 
 MIT - see [LICENSE](LICENSE) for details.