Document Roles API

[npendery]

This update adds API documentation for Roles. The following actions have been documented:

• Create a role – POST /roles
• List roles - GET /roles

Used the forbidden response generated in #465 Closes #423

[joshsmith]

@npendery some comments here that could use some work. I would look to theme in User for an example of how to do an enum.

I also think this (and other PRs) need more plain English language, even it's just a sentence or two explaining the endpoint.

[joshsmith]

The English language stuff can come in a later pass if you'd like.