[rustdoc]A wrong in documents about slice

[qingzhu521]

https://doc.rust-lang.org/std/primitive.slice.html
I think that in let x = &mut [1, 2, 3];, x is not slice. It is just a reference for primitive type (arrary)
for example:

let intarr_slice = &[&[1,2][..],&[3,4,5][..]];
let intarr_slice2 = &[&[1,2],&[3,4,5]];

that the second on is not a right statements.
against the definition of let str_slice: &[&str] = &["one", "two", "three"];
x = &mut[1,2,3][..] is slice type.

And I think it's better to add a note.

let x = [1,2,3];
let y = &x[..];

and

let x = &[1,2,3];
let y = &x[..];

these y are same.