I'm a little hesitant to do this because most tools I'm familiar with
have the config file directly in `~/`. It's also easier to describe
where to put the file if it doesn't vary across platforms. But we're
still early in the project, so let's try it and see if we get any
complaints.
I'm preparing to publish an early version before someone takes the
name(s) on crates.io. "jj" has been taken by a seemingly useless
project, but "jujube" and "jujube-lib" are still available, so let's
use those.
