Update documentation to include adapterOptions example

[rmharrison]

The addon uses urlSegments for dynamic portions of nested routes. How to pass information from the model to the functions of urlSegments is non-obvious.

As of 72c1aad, the README uses sessions.
Catch: Managing state in a singleton; bad bad. That's what the router is for.

A stackoverflow post mentions the use of query.
Catch: Query is null for most common urlFor* methods such as urlForFindAll() <-- this.store.findAll(). Must use this.store.query() or this.store.queryRecord()

I prefer snapshot.adapterOptions, as snapshot is available for all urlFor* methods.

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