minor comment update in screen editor

src/kernal/screen_m65/mega65_chrout_screen_control.s

@@ -94,3 +94,7 @@ m65_chrout_screen_ESC:
 m65_chrout_screen_BELL:
 
 	jmp m65_chrout_screen_done
+
+; XXX: implement the following functionalities according to MEGA65 book:
+; CTRL +T +Z +E +Q +G +J +U +W +B +N +M +] +I +X +K +L +[
+; ESC +@ +A +B +C +D +E +F +G +H +I +J +K +L +M +N +O +P +Q +S +T +U +V +W +X +Y +Z +1..8