Add function documentation

src/lib.rs

@@ -10,6 +10,8 @@ use game::{
     setup::{setup_balls, setup_player, setup_pseudo_random, setup_ui, setup_walls},
 };
 
+/// The initial configuration passed to the game's setup functions.
+/// Also functions as a Bevy plugin to pass the configuration into the app.
 #[derive(Parser)]
 #[command(version, about)]
 pub struct AppSettings {