Write documentation for ReadTheDocs

[aik099]

We need to write documentation and I think that https://readthedocs.org/ is the right place to do it. The only problem is that they are using reStructured Text (RST) format and not Markdown (MD), but we can work something out.

Example: http://behat-page-object-extension.readthedocs.org/en/latest/index.html