[WIP] Docs and resources for deploying on AWS EMR

[jcrist]

This PR intends to cover:

• Docs on running Dask on EMR (minimal, just install and follow the quickstart
• Docs on using our nice bootstrap action, which creates an environment, does minimal configuration, and starts a jupyter notebook server. This is basically a 1-click way to get a dask environment up and running on AWS EMR

TODO:

• Make sure everything works on EMR (no changes were needed, everything already worked :))
• Write up a nice bootstrap action script to deploy dask on EMR in a one-click way
• Write up docs on using dask on EMR

Fixes #28.

[jcrist]

Ok, an initial take on the docs is up. I'm going to merge this for now, we can update this documentation if things aren't 100% clear later.