added contributing guidelines

Author: spacedevin

CONTRIBUTING.md

@@ -0,0 +1,13 @@
+## Contributing to Tipsy
+
+##### Issues
+Found a bug? Got a suggestion? Feel free to check out the [Issue Tracker](https://github.com/tipsyphp/tipsy/issues) to make an issue.
+
+##### Pull Requests
+If you are really awesome, fix an issue by making a pull request. PRs are glady accepted on any of the projects on [tipsyphp](https://github.com/tipsyphp). When contributing to [tipsyphp/tipsy](https://github.com/tipsyphp/tipsy), please make sure your builds pass the unit tests using either [Travis CI](https://travis-ci.org/) or running the tests localy from the [Test Script](https://github.com/tipsyphp/tipsy/blob/master/tests/test.sh) using [PHPUnit](https://phpunit.de/).
+
+##### License
+Tipsy is licensed under the [MIT License](https://github.com/tipsyphp/tipsy/blob/master/LICENSE).
+
+##### More Info
+For general questions join the [Tipsy Slack](https://tipsy-slack.herokuapp.com/) channel.