Increase clarity about Hash - Eq consistency in HashMap and HashSet docs
As discussed [here](https://users.rust-lang.org/t/what-hapens-if-hash-and-partialeq-dont-match-when-using-hashmap/98052/13) the description of logic errors in `HashMap` and `HashSet` does not explicitly apply to
```text
k1 == k2 -> hash(k1) == hash(k2)
```
but this is likely what is intended.
This PR is a small doc change to correct this.
r? rust-lang/libs
0cc4b55a12