Add some simple Getting Started instructions

As a developer who wishes to contribute to this project, I would like to quickly be able to find the information necessary and perform the appropriate steps, to get up and running locally as quickly as possible.

These items include, but are not limited to:
* Which configuration elements do I need to set or update
* Twitch configuration and authentication setup (token, etc.)
* How can I test this locally behind a private IP address (i.e.: using [ngrok](https://ngrok.com))