add example for how to extract auth info from path parameters

[vlmutolo]

This is arguably one of the more common use cases for authorization. Certain resource paths will be protected, and often a dynamic piece of the path will need to be given to the authorizer.

For example, if we have a website that protects the endpoint /vlmutolo/tower-biscuit-auth/, where both vlmutolo and tower-biscuit-auth are dynamically parsed path parameters, then we need to be able to provide both of those strings to the authorizer. We'd want to end up with something like:

resource("vlmutolo/tower-biscuit-auth")