Add formal documentation

### What is the problem / feature ?

The complexity of this project is growing and as we add more *things* like a javascript front-end and more django stuff on the back, having solid documentation is going to be the only way this project can continue on and expand to other organizations.

### How did it get fixed / implemented ?

I've added a `/docs/` folder with a barebones start to sphinx documentation.  I believe the initial structure will be mostly for @devnill and I to negotiate the exact specs of the REST API, which should then be a useful resource going forward for other contributors, or even community members who are interested in accessing the volunteer data in a programatic way.

### How can someone test / see it ?

- [ ] auto build and hosting on readthedocs.org
- [ ] build the docs locally using the instructions in the README

*Here is a cute animal picture for your troubles...*

![chinese-pond-turtle](https://cloud.githubusercontent.com/assets/824194/4509438/2f5e8e74-4b20-11e4-9c4d-e8e873063159.jpg)