Update rinex2snr_cl.py

[MakanAKaregar]

Made the -mk option clearer for local RINEX data that's stored in Hatanaka format.

[kristinemlarson]

Makan - I am going to accept this - I agree with you, it was not clear that Hatanaka files were allowed in the nolook option. But please next time modify the documentation. the online snippets are not nearly long enough to give that kind of information. And the official documentation is still wrong - i.e. does not tell them Hatanaka files can be read via the -mk option. https://gnssrefl.readthedocs.io/en/latest/api/gnssrefl.rinex2snr_cl.html