No compiler warning allowed

Author: Philippe-Cholet

CONTRIBUTING.md

@@ -6,9 +6,9 @@ Please check the minimum version of Rust we use in `Cargo.toml`.
 _If you are proposing a major change to CI or a new iterator adaptor for this crate,
 then **please first file an issue** describing your proposal._
 
-To pass CI tests, you should run `cargo fmt` and it might become mandatory that
-your code changes are free of "compile warnings" and "clippy warnings"
-(see [#720](https://github.com/rust-itertools/itertools/pull/720) and [#740](https://github.com/rust-itertools/itertools/pull/740)).
+To pass CI tests, your code should be free of "compiler warnings" and "rustfmt" formatted.
+And it might become mandatory that your code changes are free of "clippy warnings"
+(see [#740](https://github.com/rust-itertools/itertools/pull/740)).
 
 No guideline about using `#[inline]` yet.