Add CONTRIBUTING doc since github now supports this.

CONTRIBUTING.md

+Contributing to Ansible
+=======================
+
+Please read the following information to learn how to contribute to this project.
+
+Branch Info
+===========
+
+   * The devel branch corresponds to the latest ongoing release
+   * Various release-X.Y branches exist for previous releases
+   * All feature work happens on the development branch.
+   * Major bug fixes will be made to the last release branch only
+   * See CHANGELOG.md for release notes to track each release.
+
+Patch Instructions
+==================
+
+Contributions to the core and modules are greatly welcome.
+
+   * Required Process:
+       * Submit github pull requests to the "ansible/devel" branch for features
+       * Fixes for bugs may also be submitted to "ansible/release-X.Y" for the last release
+       * Make sure "make tests" passes before submitting any requests.
+   * Bonus points:
+       * Joining the mailing list
+       * Fixing bugs instead of sending bug reports.
+       * Using squash merges
+       * Updating the "rst/*" files in the docs project and "docs/" manpage content
+       * Adding more unit tests
+   * Avoid:
+       * Sending patches to the mailing list directly.
+       * Sending feature pull requests to the 'release' branch instead of the devel branch
+       * Sending pull requests to mpdehaan's personal ansible fork.
+
+
+