Make "Collections are smart pointers"-idiom more beginner-friendly

[pedzed]

2.5 is not the easiest section to follow. I can't exactly describe what, but more information and examples overall could help.

[pedzed]

Moving (the contents of) the Discussion heading up would make more sense as well.

[reed9999]

Even if this issue could be a bit outdated, I agree 100%. The example is entirely aimed at a more experienced Rustacean who sees

impl<T> Deref for Vec<T> {
    type Target = [T];

    fn deref(&self) -> &[T] {
        //..
    }
}

and intuitively grasps how callers would use deref there. For the less experienced, an example of calling code would help.

On #423 I give details about my "intermediate beginner" level of Rust skill, so it's fine to tell me I should read something else first.