README: describe normalization features

[ngirard]

Hey,
I just stumbled upon Scrubcsv. Thanks for your time and dedication into this project !

I had a hard time figuring out what Scrubcsv offers after reading the README.
Browsing the tests file and running scrubcsv --help helped much, but it would be best if the README went into details into what Scrubcsv can do.
At the very least, appending the output of scrubcsv --help to the README would be an improvement.

Cheers !