message: Add some extra docs to StarlarkValue
  Summary: It's non-obvious when adding methods to StarlarkValue that they might not be called properly if the StarlarkValue impl for Wrapper is not updated. At the very least, add a comment to point people in the right direction
diff: @@ -337,6 +337,11 @@ pub trait SimpleValue: StarlarkValue<'static> + Send + Sync {}
  ///
  /// Every additional field enables further features in Starlark. In most cases the default
  /// implementation returns an "unimplemented" [`Err`].
  +///
  +/// # Note To Implementors
  +/// Any additional methods that are added to this trait also need to be added to the
  +/// [`StarlarkValue`] implementation in `crate::values::layout::avalue::Wrapper`. Otherwise,
  +/// any implementations other than the default implementation will not be run.
  pub trait StarlarkValue<'v>: 'v + AnyLifetime<'v> + AsStarlarkValue<'v> + Debug {
  /// Return a string describing the type of self, as returned by the type()
  /// function.
  