Honor option '--help'

[gvanem]

After installing the requirements with pip3.exe install -U pyModeS pyrtlsdr
and issuing a py.exe -3 pyModeS\streamer\modeslive.py --help, all I get is:

---------------------------------------------------------------------
Warning: pyrtlsdr not installed (required for using RTL-SDR devices)!
---------------------------------------------------------------------

I'd assume some sensible help regardless of some import error. But nothing.
This is one confusing package IMHO. Is it really for Windows at all?