Update cities.csv

[goldhaxx]

Added Salt Lake City, UT to cities.csv

[da-luce]

The cities.csv file is generated using a script that filters these cities with a set population cutoff. I agree that Salt Lake City should probably be included, so if you want to regenerate the file with a population threshold of 200,000, I'd be happy to accept this PR.

[goldhaxx]

@da-luce how was cities15000.txt generated?

[da-luce]

Sorry for leaving that out. GeoNames provides a zip to the file.

[da-luce]

Since cities.csv now has a population threshold of 200,000 (see filter_cities.py), Salt Lake City is now included. I confirmed this works with: astroterm -i "Salt Lake City"