Add a guide to creating a new controller

[mcmire]

It is good that we have guidelines for writing controllers, but they are very succinct. Engineers that have not worked with the core repo and are unfamiliar with the concept of controllers may find the them daunting and may even ignore them altogether. To improve the chances that people create controllers that follow our standards, we should have a gentler guide to creating a new controller (perhaps even a tutorial).

Acceptance Criteria

• A friendly how-to guide on creating a new controller exists in the docs/ directory.
• This guide provides links to the sample controllers, package guidelines, and controller guidelines.