Created CONTRIBUTING.md

Still a WIP

CONTRIBUTING.md

+# Contributing
+
+From opening a bug report to creating a pull request: every contribution is
+appreciated and welcome. If you're planning to implement a new feature or change
+the api please create an issue first. This way we can ensure that your precious
+work is not in vain.
+
+## Issues
+
+If you are having configuration or setup problems, please post
+a question to [StackOverflow](https://stackoverflow.com/search?q=ar.js).
+You can also address question to us in our [Gitter chatroom](https://gitter.im/AR-js/Lobby)
+
+**If you have discovered a bug or have a feature suggestion, feel free to create an issue on Github.**
+
+## Submitting Changes
+
+After getting some feedback, push to your fork and submit a pull request. We
+may suggest some changes or improvements or alternatives, but for small changes
+your pull request should be accepted quickly.
+
+Some things that will increase the chance that your pull request is accepted:
+
+<!--* [Write tests](./test/TODO.md) -->
+* Follow the existing coding style
+* Write a [good commit message](http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html)
+
+## Documentation
+
+The documentation is still WIP for this project all contributions are very welcomed, 
+you can contribute to documentation here [AR.js-docs](https://github.com/jeromeetienne/AR.js-docs)