docs(CONTRIBUTING.md): add contrib info file for GitHub

CONTRIBUTING.md

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+## Submitting issues
+
+If you have questions about how to use AngularJS, please direct these to the
+[Google Group][groups] discussion list or [StackOverflow][stackoverflow]. We are
+also available on [IRC][irc].
+
+### Guidelines
+
+* Search the archive first, it's likely that your question was already answered.
+* A live example demonstrating your problem or question, will get an answer faster.
+* Create one using this [template][template]
+* If you get help, help others. Good karma rulez!
+
+If your issue appears to be a bug, and hasn't been reported, open a new issue.
+Help us to maximize the effort we can spend fixing issues and adding new
+features, by not reporting duplicate issues.
+
+[stackoverflow]: http://stackoverflow.com/questions/tagged/angularjs
+[groups]: https://groups.google.com/forum/?fromgroups#!forum/angular
+[irc]: http://webchat.freenode.net/?channels=angularjs&uio=d4
+[template]: http://plnkr.co/edit/gist:3510140
+
+## Contributing to Source Code
+
+We'd love for you to contribute to our source code and to make AngularJS even
+better than it is today!
+
+ Please read the [contribution guidelines][contribute] to learn about how to submit code as well as
+ other useful info like how to build and test AngularJS code.
+
+[list]: https://groups.google.com/forum/?fromgroups#!forum/angular
+[contribute]: http://docs.angularjs.org/misc/contribute