Using my own box files in Kitchenfile

Opscode doesn't have a Debian box file yet, anyway.
(Maybe I should make these public, but I don't know if I can afford
the bandwidth.)
Change metadata and readme; bump up to 0.1.8

The README now explains what's going on a little more thoroughly.

The metadata now specifies *only* the OSs where I've seen this cookbook
work, but it does not limit the versions of those OSs.