feat: add group configuration (+)

will only check users of such group

also cleaned some code:
- Input doesn't need to be UTF-8 valid.
- Main fuction is dead-simple, very readable.
- Added some modularity.
- Add some docs on behavior details.

shell.nix

@@ -5,7 +5,7 @@
     {
       devShells.default = pkgs.mkShell {
         inputsFrom = [
-          inputs'.error's-rust-overlay.devShells.rust-nightly
+          inputs'.error's-rust-overlay.devShells.rust
         ];
 
         shellHook = ''
@@ -20,20 +20,18 @@
           done
 
           if [ -z "$QEMU_BRIDGE_HELPER_PATH" ]; then
-            printf "\033[1;33m%s\033[0m\n" \
-              "WARN: 'qemu-bridge-helper' not found, make sure it is installed and the nix shell hook is looking for it" >&2
+            printf "\033[1;33m%s%s\033[0m\n" \
+              "WARN: 'qemu-bridge-helper' not found, make sure it is " \
+              "installed and the nix shell hook is looking for it" >&2
           fi
         '';
 
         packages = with pkgs; [
-          # cargo
           curl
           delta
           git
           nixfmt
           pam
-          # rust-analyzer
-          # rustc
         ];
       };
     };