Reverse parenting order of Sprite and AnimationPlayer in tutorial

The docs had a sprite as the child of the player, then *immediately* after
says to not do that. Why mislead the reader at all and not just do it
the better way from the start? There nothing really gained from the
sprite being a child here, not even simplicity.

(cherry picked from commit f2ac9f8ab8)

tutorials/animation/introduction.rst

@@ -105,8 +105,8 @@ Tutorial: Creating a simple animation
 Scene setup
 ~~~~~~~~~~~
 
-For this tutorial, we'll create an AnimationPlayer node and a sprite node as its
-child.
+For this tutorial, we'll create a Sprite node with an AnimationPlayer as
+its child. We will animate the sprite to move between two points on the screen.
 
 .. figure:: img/animation_animation_player_tree.png
    :alt: Our scene setup