Update README.md

Author: cybergalactic

README.md

@@ -4,7 +4,7 @@ The Python Vehicle Simulator is a supplement to the Matlab MSS (Marine Systems S
 
  Source files:
  /src/python_vehicle_simulator/ 
-  main.py - MAIN PROGRAM (python terminal command >>python3 main.py)
+  main.py - MAIN PROGRAM (terminal command >>python3 main.py)
   control.py - feedback control systems
   gnc.py - generic GNC functions
   guidance.py - guidance functions