Document in README how to install and use

[gnprice]

The tool itself has a pretty nice --help output, once you get to running it at all.

When coming upon the repo here on GitHub, you don't see that and instead you see the README. It'd be really helpful for that to (a) say how to install it (it's trivial, in fact -- copy the files into /usr/local/bin/ or elsewhere on your PATH -- but that needs to be written down), and (b) maybe just have a copy of the --help output, so you can see what you'll get.