Docs: show off "dot notation" attribute access when validating an entire dict at once

It would be much prettier to be able to do `config.something[0].name.get()` instead of using string keys for everything. I realize there's the concern of keys being masked by object attributes, but I feel like it's worth it (you can still use strings in those cases). And that conflict could be partially be alleviated by adding an API reference so people will be able more aware of keys that will be masked.