Add extra clarification for nested resources

Taken from mavilein's comments on Stack Overflow: http://stackoverflow.com/questions/14973556/what-is-the-difference-between-a-route-and-resource-in-new-router-api
With some edits I would happily merge.

```
The route, controller, and view class names for the comments resource are not prefixed with `Post`. Resources always reset the namespace, ensuring that the classes can be re-used between multiple parent resources and class names don't get longer the deeper nested the resources are.
```