Auto merge of #30146 - steveklabnik:doc_string_intro, r=brson
Auto merge of #30146 - steveklabnik:doc_string_intro, r=brson

Part of #29376

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