scripts/README.md typo

[Steve-Albers]

Hi - as I learn how to install and run 'pyshdom' I see that the command below within scripts/README.md has a typo. The correct spelling should probably be "num_veff" instead of "num veff".

python scripts/generate_mie_tables.py
--start_reff 4.0 --end_reff 25.0 --num_reff 50 --start_veff 0.01 --end_veff 0.2 --num veff 50
--radius_cutoff 65.0 --wavelength 0.355 0.38 0.445 0.47 0.555 0.66 0.865 0.935

[Steve-Albers]

Another suggestion would be to change the above list of wavelengths to use 0.672 instead of 0.66 to be consistent with the other examples.