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 = "ssh://gi...@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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