Rollup merge of #43790 - steveklabnik:rustdoc-passes, r=QuietMisdreavus
Rollup merge of #43790 - steveklabnik:rustdoc-passes, r=QuietMisdreavus

Write the "passes" chapter of the rustdoc book

cc #42322

r? @rust-lang/docs

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