add docs about native overlay

Author: matiqo15

crates/bevy_dev_tools/src/fps_overlay.rs

@@ -14,6 +14,10 @@ use bevy_ui::node_bundles::TextBundle;
 #[derive(Default)]
 /// A plugin that adds an FPS overlay to the Bevy application.
 /// Warning: This plugin will add [`FrameTimeDiagnosticsPlugin`] if it wasn't added before.
+///
+/// Note: It is recommended to use native overlay of the rendering APi when possible. You can do
+/// this by:
+/// - **Metal**: setting env variable `MTL_HUD_ENABLED=1`
 pub struct FpsOverlayPlugin {
     /// Starting configuration of overlay, this can be later be changed through [`FpsOverlayConfig`] resource.
     pub config: FpsOverlayConfig,