Rollup merge of #90438 - GuillaumeGomez:doc-show-coverage, r=camelid
Rollup merge of #90438 - GuillaumeGomez:doc-show-coverage, r=camelid

Clean up mess for --show-coverage documentation

It was somewhat duplicated for some reasons... Anyway, this remove this duplication and clean up a bit.

r? ```@camelid```

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