Include "Theme Overrides" to font size update instruction

Co-authored-by: Yuri Sizov <[email protected]>

getting_started/first_2d_game/06.heads_up_display.rst

@@ -48,7 +48,7 @@ well. There is a font file included in the game assets called
 Once you've done this on the ``ScoreLabel``, you can click the down arrow next
 to the Font property and choose "Copy", then "Paste" it in the same place
 on the other two Control nodes.
-Set "Font Size" property of the ``ScoreLabel``. A setting of ``64`` works well.
+Set the "Font Size" property of the ``ScoreLabel`` under "Theme Overrides > Font Sizes". A setting of ``64`` works well.
 
 .. image:: img/custom_font3.png