Add a section about automatic code formatting in CONTRIBUTING.md
Add a section about automatic code formatting in CONTRIBUTING.md

emilio/rust-bindgen,emilio/rust-bindgen,emilio/rust-bindgen,jdub/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,jdub/rust-bindgen,jdub/rust-bindgen,jdub/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,rust-lang/rust-bindgen