make alien a collider

src/main.rs

@@ -72,6 +72,7 @@ fn main() {
     }));
 
     app.add_plugins(PhysicsPlugins::default());
+    app.add_plugins(PhysicsDebugPlugin::default());
 
     // bevy_flycam setup so we can get a closer look at the scene, mainly for debugging
     app.add_plugins(PlayerPlugin);