ParseIntError docs should mention other integer parsing functions

[lolbinarycat]

Location

https://doc.rust-lang.org/stable/std/num/struct.ParseIntError.html

Summary

Currently it says it is used for parse_str_radix, but it is also used as the FromStr error type.

It will also be used by from_ascii and from_ascii_radix, so ideally the new docs should be worded in a way that is not easily misinterpreted as an exhaustive list.

[GrigorenkoPV]

@rustbot claim