Improve help messages

In this, the short help, we want to provide an abbreviated help message for the user. (i.e. use `--help` for more verbose help). Maybe we should get rid of the `SYNOPSIS` heading right above, since it's a bit overloaded with the description right below. (i had thought it was ok since "synopsis" also means "summary", but since it's very specific in man-page speak, we could get rid of the heading)