Add C# instructions for Your first game (#5474)

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

getting_started/first_2d_game/03.coding_the_player.rst

@@ -425,7 +425,8 @@ We want ``Player`` to detect when it's hit by an enemy, but we haven't made any
 enemies yet! That's OK, because we're going to use Godot's *signal*
 functionality to make it work.
 
-Add the following at the top of the script, after ``extends Area2D``:
+Add the following at the top of the script. If you're using GDScript, add it after
+``extends Area2D``. If you're using C#, add it after ``public class Player : Area2D {``:
 
 .. tabs::
  .. code-tab:: gdscript GDScript