- cli: the subcommand is optional; without one, sausage runs ./world and
runs init first when ./world is not a world yet (test: cli/tests/cli.rs).
So `nix run git+https://gitea.surma.technology/surma/sausage` works.
- flake: .#loop without a folder runs bare sausage.
- README: mention the bare command and the bare loop.
