Add description for env var

telematic_system/docker-compose.units.yml

@@ -26,7 +26,7 @@ services:
     - VEHICLE_BRIDGE_LOG_ROTATION_SIZE_BYTES=2147483648 #2 gigabytes
     - VEHICLE_BRIDGE_LOG_HANDLER_TYPE=console #console: Print logs on console; file: Save logs to file; all: Prints logs on console and file
     - VEHICLE_BRIDGE_EXCLUSION_LIST= ${VEHICLE_BRIDGE_EXCLUSION_LIST} #OPTIONAL variable to set a comma separated list of topics not available to publish, leave empty if none
-    - IS_SIM=False
+    - IS_SIM=False #OPTIONAL variable to treat incoming messages as coming from simulation env.  In this case The bridge will use system time as message timestamp. Defaults to False
 
   streets-nats-bridge:
     build: