Added some more information to --help

[ez-me]

I mostly use --help for commands, and only use the manpages (or even the docs, or code) if I need something very specific. I hope this can aid folks that mostly use --help as well

Copied mostly from the manpage (and pdf) that -0 is no compression, the default is -6, and that for both -I and -J the default is 15.