Strings chapter: &String doesn't actually coerce to &str

"Strings will coerece into &str with an &:

```
fn takes_slice(slice: &str) {
    println!("Got: {}", slice);
}

fn main() {
    let s = "Hello".to_string();
    takes_slice(&s);
}
```

"
This example should have `&*s` rather than `&s`, and the line above it should be reworded, since this isn't a coercion. (Note coerce is misspelled as coerece)
