Rollup merge of #147373 - cyrgani:cyrgani-patch-1, r=ibraheemdev

give a better example why `std` modules named like primitives are needed

A small update to the `std` `lib.rs` introduction to replace mentions of `std::i32` (never needed) with `std::char` (sometimes needed).
Related to rust-lang/rust#146882.

Author: Zalathar