Clarify that --id and --ignore args take column names
Clarify that --id and --ignore args take column names

The other tool I was using until I found this (csvdiff) uses column numbers, and it took me a while to figure out that this one was using names. 🙂
paulfitz/daff,paulfitz/daff,paulfitz/daff,paulfitz/daff,paulfitz/daff,paulfitz/daff,paulfitz/daff,paulfitz/daff,paulfitz/daff