Adding simple README. fixes #1

Just a simple README.md based of Ben's work in the main processing repo.

It reads:

Processing Web Site
==========

This is the official source code for the [processing.org Web site](http://processing.org), including the examples and the reference.

If you have found an error in the Processing Web site, examples, or the reference, you can file it here under the ["issues" tab](https://github.com/processing/processing-web/issues).

The [processing](https://github.com/processing/processing) repository contains the source code for Processing itself. (Please use that link to file issues regarding the Processing software.)

<!-- Thanks Ben, Casey, and all the contributors for all things Processing! -->