Add Development Guide

[andrewkrug]

For contribution friendliness we should have a development / getting-started guide.

[gene1wood]

Include

• Diagram / drawing / description of the system, it's components and how the interact with each other
• The workflow to take a modification in some piece of source code and move it all the way through to be deployed in production

[andrewkrug]

We've already got architecture diagrams in the docs/ folder.

I'll add a development guide though.

[andrewkrug]

In looking at the README I actually think this is well covered. Can you give a glance and see where the gaps are?