Add an option for automatically running SuperDirt for the duration that the `devShell` is active

[mitchmindtree]

See the forum discussion on options for how to approach this here:

https://discourse.nixos.org/t/how-to-run-a-service-only-while-a-devshell-is-open/19752?u=mindtree

[mitchmindtree]

An alternative might be to run superdirt automatically using the editor plugin, similarly to how the ghci interpreter is run automatically. Should solve #2 first to ensure that supercollider can be configured as needed from nix.

[mitchmindtree]

The Vim plugin approach is supported as of #12. Will leave this open as it might still be worth considering the devShell approach, even if only as an option.