Added a reminder about the port argument.

5-Add-virtual-motors.md

@@ -375,6 +375,8 @@ Options:
 
 #### 5.10.2 Start servery.py in a different terminal window
 
+Reminder: the port argument passed to the `-p` option must match the value of `VMC_PORT` chosen in [step 5.7.2](5-Add-virtual-motors.md#572-modify-iocshvmccmd)
+
 ```
 $ xterm -e "${SUPPORT_DIR}/motorVMC/python/server.py -p 33333" &
 ```