Document OAuth process: The general overview

[hillairet]

Ideally the SPyLib documentation is more than just saying how to use SPyLib but also another and hopefully better version on how to use the Shopify APIs.

A more readable and to the point explanation of the OAuth process would be neat. I can then be referenced in the rest of the documentation.
A good old sequence diagram to give the big picture would be good.
This should be a reference document looked at to learn or remember the steps in the OAuth.