Add reveal_index.html for use with reveal.js

## Install reveal.js

  - Follow the full installation instructions here: https://github.com/hakimel/reveal.js#full-setup

## Creating the markdown

The marker ``!`` will split your markdown across slides vertically, in a sub-topic kind of way.

To start a new topic entirely, use ``<!>``.

## Running the demo.

 - Copy ``reveal_index.html`` into the cloned ``reveal.js`` folder you installed and name it ``index.html``.
 - Copy your markdown file into the same folder.
 - Ensure that the name of the markdown file referenced by ``data-markdown`` is correct.
 - Run ``grunt serve``.