message: Document that `this` is special in #[starlark_module]
  Summary: For the moment, we don't rely on this, but set the rules so we can exploit it later.
diff: @@ -90,8 +90,10 @@ use syn::*;
  /// }
  /// ```
  ///
  -/// Parameters operate as named parameters of a given type, with five possible tweaks:
  +/// Parameters operate as named parameters of a given type, with six possible tweaks:
  ///
  +/// * `this` (or `_this`) as the first argument means the argument is passed as a
  +/// bound method value, e.g. in `a.f(...)` the `a` would be `this`.
  /// * `args` means the argument is the `*args`.
  /// * `kwargs` means the argument is the `**kwargs`.
  /// * `ref name` means the argument must be passed by position, not by name.
  