rust/src/docs/clone_double_ref.txt

### What it does
Checks for usage of `.clone()` on an `&&T`.

### Why is this bad?
Cloning an `&&T` copies the inner `&T`, instead of
cloning the underlying `T`.

### Example
```
fn main() {
    let x = vec![1];
    let y = &&x;
    let z = y.clone();
    println!("{:p} {:p}", *y, z); // prints out the same pointer
}
```