Add support and contribution guidelines

Author: amacneil

README.md

@@ -384,6 +384,26 @@ web server (PHP 5.4+):
 
 For more information, see the [example application directory](https://github.com/adrianmacneil/omnipay/tree/master/example).
 
+## Support
+
+If you are having general issues with Omnipay, we suggest posting on
+[Stack Overflow](http://stackoverflow.com/). Be sure to add the
+[omnipay tag](http://stackoverflow.com/questions/tagged/omnipay) so it can be easily found.
+
+If you believe you have found a bug, please report it using the [GitHub issue tracker](https://github.com/adrianmacneil/omnipay/issues),
+or better yet, fork the library and submit a pull request.
+
+## Contributing
+
+* Fork the project.
+* Make your feature addition or bug fix.
+* Add tests for it. This is important so I don't break it in a future version unintentionally.
+* Commit just the modifications, do not mess with the composer.json or CHANGELOG.md files.
+* Ensure your code is nicely formatted in the [PSR-2](https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-2-coding-style-guide.md)
+  style and that all tests pass.
+* Send the pull request.
+* Check that the [travis build](https://travis-ci.org/adrianmacneil/omnipay) passed. If not, rinse and repeat.
+
 ## Feedback
 
 **Please provide feedback!** We want to make this library useful in as many projects as possible.