Add explanation: why we use Node and not Node2D (#5530)

* Add explanation: why we use Node and not Node2D

Co-authored-by: Hugo Locurcio <[email protected]>

getting_started/first_2d_game/05.the_main_game_scene.rst

@@ -5,9 +5,12 @@ The main game scene
 
 Now it's time to bring everything we did together into a playable game scene.
 
-Create a new scene and add a :ref:`Node <class_Node>` named ``Main``. Ensure you
-create a Node, **not** a Node2D. Click the "Instance" button and select your
-saved ``Player.tscn``.
+Create a new scene and add a :ref:`Node <class_Node>` named ``Main``.
+(The reason we are using Node instead of Node2D is because this node will
+be a container for handling game logic. It does not require 2D functionality itself.)
+
+Click the **Instance** button (represented by a chain link icon) and select your saved
+``Player.tscn``.
 
 .. image:: img/instance_scene.png