Add comments.

examples3d/primitives3.rs

@@ -25,7 +25,7 @@ pub fn init_world(testbed: &mut Testbed) {
     colliders.insert(collider, handle, &mut bodies);
 
     /*
-     * Create the cubes
+     * Create the primitives
      */
     let num = 8;
     let rad = 1.0;