Added a pre-built disk

Added Penetrator.dsk - an Apple II ready disk for emulators

Author: StewBC

Penetrator.dsk

@@ -18,6 +18,9 @@ attract mode, and the fireworks.
 Here's a video of Oliver Schmidt's son, Pascal, playing the game on real
 hardware: https://www.youtube.com/watch?v=rXC2JKuN594
 
+There's also a pre-built Apple II disk of the project, Penetrator.dsk in the
+root folder.  This can be played directly in emulators.
+
 3. TECHNICAL DETAILS
 
 The game is written in 6502 assembly using the ca65 assembler.