Rollup merge of #36241 - Cobrand:contributing-md, r=steveklabnik
Rollup merge of #36241 - Cobrand:contributing-md, r=steveklabnik

doc: Contributing.md: Added mention of `make tidy`

r? @steveklabnik

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