-newport: More comments, nw

src/devices/bus/gio64/newport.cpp

@@ -27,6 +27,10 @@
 	  FIFOs are always empty. Thus the performance of an emulated
 	  Newport board is likely to be better than real life in scenes
 	  that would otherwise be drawing-bound.
+	- The REX3 emulation currently handles a bunch of functionality
+	  that should be the responsibility of RO1 and RB2. However,
+	  emulating it properly would bring down the emulation speed
+	  for not much practical benefit.
 
 *********************************************************************/