Initial commit of Rec Room docs in Markdown format

- Will eventually move docs to MDN App Center - Quick Start, but
  we need them on GitHub as well.
Here's my suggested change:

Rec Room uses Ember.js as the framework to build your app’s controllers, models, and views. While you don’t need to know Ember.js (our documentation will walk you through the basics you’ll need), some previous knowledge would be useful. You can always refer to the excellent [Ember.js guides](http://emberjs.com/guides/). They do a good job explaining the structure of Ember apps, especially in relation to the [MVC (Model View Controller) design pattern](http://en.wikipedia.org/wiki/Model-view-controller).

We also provide a brief introduction to important Ember concepts in [Appendix 2: A Brief Introduction to Ember](A2 - A Brief Introduction to Ember.md).