One liner installation (Linux)

[scooter-dangle]

Starting with Linux since it's easy (and we'll likely have a pre-built binary for it soon).

Note: This should also modify the fish_update_completions function to preferentially call our compiled binary.

We've technically hit our MVP goals, but this is the last step before we'd want to advertise the project as an alternative. I.e., what's the install process if we say this is now usable?

[pickfire]

I think we can first provide tarballs and bundle for linux distributions, but for the build it is better to cargo build --release, as for consumers they can download the built artifacts we store in github and take it in locally.