Added contribution guidelines

CONTRIBUTING.md

@@ -0,0 +1,37 @@
+## Want to Contribute?
+
+Found an issue? Thank you for helping out by reporting it. Please describe the
+problem, what you tried, what you expected to see, and what you actually
+experienced. Please [re-read the documentation](http://timeago.yarp.com/) to
+make sure you're using the API as designed, but if you found something that's
+broken, we really appreciate your efforts in letting us know. Bonus points for
+submitting a failing test case to help us diagnose and potentially fix the
+issue.
+
+## Want to Contribute?
+
+Awesome. We love help, but before getting started, please read:
+
+**[Don't "Push" Your Pull Requests](http://www.igvita.com/2011/12/19/dont-push-your-pull-requests/)**
+
+## Ready for a Pull-Request?
+
+1. Fork the repo.
+
+2. Run the tests. Run `rake` or open `open test/index.html`. We only take pull
+   requests with passing tests, and it's great to know that you started from a
+   clean slate.
+
+3. Add a test for your change. Only refactoring and documentation change
+  require no new tests. If you are adding functionality or fixing a bug, we
+  need a test!
+
+4. Make the test pass.
+
+5. Push to your fork (hopefully this comes from a topical branch) and submit a
+   pull request.
+
+At this point you're waiting on us. Please keep in mind that OSS maintainers
+are often very busy. We'll do our best to at least comment on issues and
+pull-requests as soon as possible, but sometimes life gets in the way.  We may
+also suggest some changes or improvements or alternatives.