Unable to define shebang for guix shell file

[Jacob Hrbek]

I am unable to define a guix shell file with shebang to decrease the complexity needed in the repository managing (so that i can just do ./path/to/guix.scm for guix to invoke `guix shell -f ./path/to/guix.scm` instead of having to sanitize the runtime) as the issue is that POSIX shebang allows only one argument and due to the way we handle reproducibility the shebang has to be `#!/usr/bin/env <command>`

Proposing to integrate guix-shell for this purpose (inspired by NixOS) e.g.

```nix
#!/usr/bin/env nix-shell
# NixOS shell configuration to bootstrap the required dependencies to run and use the editor

# NOTE(Krey): This is designed to contain ONLY editor-specific configuration **NOT** project specific

let
    nivSources = builtins.fetchGit {
        url = ""mailto:gitea@git.dotya.ml">gitea@git.dotya.ml:RiXotStudio/std-niv.git";
        rev = "7664e29d8ba174cde2e4ff98331fa12e18258b7a"; # 24/10/2021-EU 23:57:10 CEST
        ref = "central";
    };
in {
    sources ? import "${nivSources}/sources.nix",
    nixpkgs ? import sources.nixpkgs {},
}:
with nixpkgs;
    stdenv.mkDerivation {
        name = "RiXotStudio_emacs-config";
        buildInputs = [
            fira-code # Default font with liqurature support
            emacs # Editor
        ];

    }
```

-- Jacob "Kreyren" Hrbek

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