Update run.py for Windows users

[ghabault]

To avoid Windows users having this Runtime error:

    An attempt has been made to start a new process before the
    current process has finished its bootstrapping phase.
    This probably means that you are not using fork to start your
    child processes and you have forgotten to use the proper idiom
    in the main module:

        if __name__ == '__main__':
            freeze_support()
            ...
    The "freeze_support()" line can be omitted if the program
    is not going to be frozen to produce an executable.```