Rollup merge of #37343 - bluss:write-doc, r=GuillaumeGomez
Rollup merge of #37343 - bluss:write-doc, r=GuillaumeGomez

Add documentation for Read, Write impls for slices and Vec

The Write imps for &[u8] and Vec<u8> are quite different, and we need this to
be reflected in the docs.

These documentation comments will be visible on the respective type's
page in the trait impls section.

graydon/rust,GBGamer/rust,graydon/rust,GBGamer/rust,GBGamer/rust,graydon/rust,aidancully/rust,GBGamer/rust,graydon/rust,aidancully/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,aidancully/rust,aidancully/rust,graydon/rust,GBGamer/rust,graydon/rust,aidancully/rust,GBGamer/rust