Rollup merge of #45648 - tbu-:pr_doc_unix_ext, r=estebank
Rollup merge of #45648 - tbu-:pr_doc_unix_ext, r=estebank

Update doc comment for the Unix extension module

It was a bit outdated, claimed to be able to do less than it actually
could.

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