Auto merge of #34725 - GuillaumeGomez:doc_slice, r=steveklabnik
Auto merge of #34725 - GuillaumeGomez:doc_slice, r=steveklabnik

Improve slice docs

Fixes  #29337.

r? @steveklabnik

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