Mismatched types error in the first example of pointers

```
let x: u8 = 1234521; // requires 1 byte(8 bits) to store "x" in memory
let y: &u128 = &x; // In a 64 bit architecture this will require 64 bits to store "y" in memory
let z: &&u128 = &y; // same bits as y
```

I'm not sure if casting x to u128 is the better way...

Start with the first pointers example containing x, y, and z and reproduce the compiler's mismatched-types error. Determine the intended pointer types and update the example so it compiles, then verify that the memory-size explanation matches the corrected code.

Written by the indexing model from the issue text.