Their best deployment/installation instructions are for Macs, and for Linux they suggest things like nix-shell or flatpak, rather than straight-up packages for the popular distributions/package management systems. That's my reading of things, anyway.
Running `./mach package` will create a tarball you can use easily in any distribution. Not perfect, but I would say good enough at this stage of the project - remember Servo is not a browser, it's a browser runtime that needs to be embedded. The `servoshell` itself is just a basic example to show how the embedding works.
