Missing documentation about how to select objects

[Leo Arias]

On the autopilot tutorial we have a section about writing and using custom proxy objects. We are missing one section before that, to explain how to select items using the default proxy objects.

The methods for selection are properly documented in the code, so this could be like making a summary of that part of the API.

From rickspencer:

<rickspencer3> elopio, I feel like AP would benefit from a task hierarchy
<rickspencer3> like "how to grab items"
<rickspencer3> etc...