js-sys: Document that new bindings should take JS things by shared ref

crates/js-sys/src/lib.rs

@@ -42,6 +42,9 @@ use wasm_bindgen::prelude::*;
 // * Add a new `#[test]` into the appropriate file in the
 //   `crates/js-sys/tests/wasm/` directory. If the imported function or method
 //   can throw an exception, make sure to also add test coverage for that case.
+//
+// * Arguments that are `JsValue`s or imported JavaScript types should be taken
+//   by reference.
 
 #[wasm_bindgen]
 extern "C" {