README updates regarding the dual VT100 terminal demo

devices/pc8080/machine/README.md

@@ -10,5 +10,7 @@ PC8080 Machine Configurations
 The following 8080-based machines are currently available:
 
 * [8080 Exerciser](exerciser/)
-* [Space Invaders (1978)](invaders/)
-* [DEC VT100 Terminal](vt100/)
+* [Space Invaders (1978)](invaders/) (with [Debugger](invaders/debugger/))
+* [DEC VT100 Terminal](vt100/) (with [Debugger](vt100/debugger/))
+
+And check out the [Dual VT100 Terminals](vt100/dual/) for a demo of two PCjs machines communicating over a *virtual* serial connection. 

devices/pc8080/machine/vt100/dual/README.md

@@ -16,6 +16,12 @@ machines:
 Dual VT100 Terminals
 --------------------
 
+This is a test of two [VT100 Terminals](../) whose serial ports are *virtually* connected, so anything you type in the first
+terminal should appear on the screen of the second, and vice versa.  Click or tap on the screen of the desired terminal before
+you begin typing.
+
+If either terminal becomes LOCKED, press the SET-UP key (mapped to your F9 function key) twice to unlock it. 
+
 {% include machine.html id="vt100a" %}
 
 {% include machine.html id="vt100b" %}