message: New contribution guidelines
  Updated README.md and added CONTRIBUTING.md
diff: @@ -90,6 +90,14 @@ client.httpClient = httpClient;
  If you have any problems, questions or suggestions, create an issue here or send your inquiry to support@adyen.com.
  +## Contributing
  +We strongly encourage you to join us in contributing to this repository so everyone can benefit from:
  +* New features and functionality
  +* Resolved bug fixes and issues
  +* Any general improvements
  +
  +Read our [**contribution guidelines**](CONTRIBUTING.md) to find out how.
  +
  ## Licence
  MIT license. For more information, see the LICENSE file.
  