Attract.py alone stops without nice message

[Pierre Poulain]

When loading alone (without argument), Attract.py returns an (not user friendly) message:
---------------------------------------------------------------------------
Traceback (most recent call last):
  File "./Attract.py", line 188, in <module>
    receptor_name=args[0]
IndexError: list index out of range
---------------------------------------------------------------------------
Could we have a message briefly explaining arguments required by Attract.py and also showing the actual version number?