Add docs for integrating new services

[rosshadden]

This should be approached from the viewpoint of somebody wanting to add their own project.

• Should discuss JavaScript, Clojure, and platform-agnostic environments.
• We can use Authorization and Pricing as references, either visibly or just for writing the docs.
• Should detail just existing and getting requests/schemas proxied (Authorization)
• Should detail extending other schemas and adding custom resolvers (Pricing)