CONTRIBUTING.md

## Contributing to Spark

*Before opening a pull request*, review the 
[Contributing to Spark guide](http://spark.apache.org/contributing.html). 
It lists steps that are required before creating a PR. In particular, consider:

- Is the change important and ready enough to ask the community to spend time reviewing?
- Have you searched for existing, related JIRAs and pull requests?
- Is this a new feature that can stand alone as a [third party project](http://spark.apache.org/third-party-projects.html) ?
- Is the change being proposed clearly explained and motivated?

When you contribute code, you affirm that the contribution is your original work and that you 
license the work to the project under the project's open source license. Whether or not you 
state this explicitly, by submitting any copyrighted material via pull request, email, or 
other means you agree to license the material under the project's open source license and 
warrant that you have the legal authority to do so.