Rollup merge of #35181 - GuillaumeGomez:vec_doc, r=steveklabnik
Rollup merge of #35181 - GuillaumeGomez:vec_doc, r=steveklabnik

Add doc example for Vec

Fixes #29380.

r? @steveklabnik

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