Ownership guide

This is a work in progress, but this should get *extensive* review, so I'm putting it up early and often.

This is the start of a draft of the new 'ownership guide,' which explains ownership, borrowing, etc. I'm feeling better about this framing than last time's, but we'll see.
A very minor point but I feel like "ideal" is not the right word here, what would be "ideal" in that context? Maybe you mean "interesting", "practical" or "useful"?