Instead of keeping this in my ~/.profile, I'm going to define it in .envrc.
What I still don't know is how functions like `getenv` are supposed to interact
with direnv. I suppose maybe they aren't? Right now, when I call
`(getenv "DOTFILES")` from Emacs, it's `nil`, which I understand. Hopefully the
more I use direnv, the more reasonable expectations I'll have.