Add note to manual

peternewell · peternewell · commit f81987ba6826 · 2021-08-13T15:14:17.000+10:00
diff --git a/Source/Documentation/Manual/physics.rst b/Source/Documentation/Manual/physics.rst
@@ -2867,6 +2867,8 @@ MaxAuxilaryChargingRate and EmergencyResChargingRate.
 - ``Engine(ORTSBrakePipeTimeFactor`` -- Time in seconds for a difference in
   pipe pressure between adjacent cars to equalize to about 1/3
   (default .003).
+- ``Engine(AirBrakeMaxMainResPipePressure`` -- Pressure in Main Reservoir 
+  Pipe for twin pipe braking systems (default = Main Reservoir Pressure).
 
 .. _physics-retainers:
 
