Add warning for NEEDLESS_PASS_BY_REF_MUT lint about the fact that it changes API

Author: GuillaumeGomez

clippy_lints/src/needless_pass_by_ref_mut.rs

@@ -22,6 +22,9 @@ declare_clippy_lint! {
     /// ### What it does
     /// Check if a `&mut` function argument is actually used mutably.
     ///
+    /// Be careful if the function is publically reexported as it would break compatibility with
+    /// users of this function.
+    ///
     /// ### Why is this bad?
     /// Less `mut` means less fights with the borrow checker. It can also lead to more
     /// opportunities for parallelization.