Edit librustc_lexer top-level docs
Edit librustc_lexer top-level docs

Add link to librustc_parse::lexer

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