AntennaTracker: added a note on simulating an antenna tracker

Tools/AntennaTracker/AntennaTracker.txt

@@ -171,3 +171,23 @@ wp sethome
 
 AntennaTracker will now remember this as its HOME location whenever it is
 started.
+
+Simulating an antenna tracker
+-----------------------------
+
+To run a full antenna tracker simulation with a simulated APM:Plane as
+the vehicle, cd to the ArduPlane directory and run this:
+
+  ../Tools/autotest/sim_arduplane.sh -T --aircraft test
+
+The -T flag tells sim_arduplane.sh to start an entenna tracker
+simulator and also start a virtual antenna tracker in a window.
+
+To start the antenna tracker running run "tracker start" in the
+mavproxy window.
+
+To then connect to your antenna tracker with mavproxy you would run:
+
+  mavproxy.py --master tcp:127.0.0.1:5770
+
+then you can configure it as needed.