Document that window::Action::Move is unsupported on Wayland

https://docs.rs/winit/latest/winit/window/struct.Window.html#method.set_outer_position
notes that this isn't supported on Wayland.

Wayland by design doesn't allow applications to position windows
arbitrarily. GTK4 in comparison removed `gtk_window_move()` (which
naturally didn't work on Wayland).

native/src/window/action.rs

@@ -13,6 +13,8 @@ pub enum Action<T> {
         height: u32,
     },
     /// Move the window.
+    ///
+    /// Unsupported on Wayland.
     Move {
         /// The new logical x location of the window
         x: i32,