Guide: pointers

This is the next section of the guide, and it's on pointers. It's not done yet, as I need to write the section on ownership and borrowing, but I figured I'd share the rest now, to get feedback on the rest of it while I take some time to get that right.
Or maybe, "Boxes are the sole owner of their contents," or "Boxes have unique ownership of their contents."? I like that last one the least, but it uses the same terminology...