Contributing to Merchant
While there is no requirement for you to contribute your new gateway code or changes back to the upstream project, you can play a good samaritan by contributing back to the project and helping scores of people.
Here are the steps to follow to contribute back to Merchant:
Fork the project from it's github page.
Make the changes in your fork.
File an issue at the github page and enclose a pull request.
If you want to include a new gateway, we request you to include a few tests (probably using the current tests as a template).
Don't forget to add yourself to the CONTRIBUTORS.txt file before opening an issue.