Mention DynamicSceneBuilder in scene example (#10441)

# Objective

Make ```DynamicSceneBuilder``` more visible to new bevy learners!
```DynamicSceneBuilder``` is likely to be the most appropriate tool to use when creating dynamic scenes in all but the simplest scenarios. However, it's not mentioned in the scene example. This PR aims to fix this.

## Solution

I've modified the comment above where the ```DynamicScene``` is created to note that ```DynamicSceneBuilder``` can also be used to create the scene. I believe this is the best approach to introduce ```DynamicSceneBuilder``` without adding additional complexity to the example.

examples/scene/scene.rs

@@ -118,7 +118,8 @@ fn save_scene_system(world: &mut World) {
     scene_world.spawn(ComponentA { x: 3.0, y: 4.0 });
     scene_world.insert_resource(ResourceA { score: 1 });
 
-    // With our sample world ready to go, we can now create our scene:
+    // With our sample world ready to go, we can now create our scene using DynamicScene or DynamicSceneBuilder.
+    // For simplicity, we will create our scene using DynamicScene:
     let scene = DynamicScene::from_world(&scene_world);
 
     // Scenes can be serialized like this: