Auto merge of #3579 - matthiaskrgr:tool_lints, r=flip1995
Auto merge of #3579 - matthiaskrgr:tool_lints, r=flip1995

update CARGO_CLIPPY_HELP string to suggest tool lints.

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