update outdated images and add clarification

getting_started/first_2d_game/03.coding_the_player.rst

@@ -104,6 +104,11 @@ value written in the script.
 
 .. image:: img/export_variable.webp
 
+Your ``player.gd`` script should already contain
+a ``_ready()`` and a ``_process()`` function.
+If you didn't select the default template shown above,
+create these functions while following the lesson.
+
 The ``_ready()`` function is called when a node enters the scene tree, which is
 a good time to find the size of the game window: