Adding a CONTRIBUTING document

Adding a CONTRIBUTING document to take advantages of this:
https://github.com/blog/1184-contributing-guidelines

CONTRIBUTING.md

@@ -0,0 +1,14 @@
+Contributing to Katello
+=======================
+
+As an open-source project, we enjoy working with the community. We've developed
+some guidelines though for contributing to Katello. Please see our
+[development guidelines](https://fedorahosted.org/katello/wiki/DevProcess).
+Also, make sure your code conforms to our style guidelines:
+
+* [Ruby guidelines](https://fedorahosted.org/katello/wiki/RubyCodeConventions)
+* [Javascript guidelines](https://fedorahosted.org/katello/wiki/JavascriptCodeConventions)
+* [Python guidelines](https://fedorahosted.org/katello/wiki/PythonCodeConventions)
+
+Be sure to check out our README and let us know on our mailing list or IRC
+if you have any questions.