I think the mutability docs have one confusing part:
let mut x = 5;This is a mutable variable binding. When a binding is mutable, it means you’re allowed to change what the binding points to.
And then it says:
If you want to change what the binding points to, you’ll need a mutable reference:
Which is exactly the same phrase ("to change what the binding points to"). 
I understand that the context is different, but this is so central and sometimes subtle (as the docs also say) that maybe another phrasing could be better.
The examples help a lot, though.