[doc] add app doc to serve doc

'nix run .#doc' will open documentaion in browser and update on
filechange

doc/.gitignore

@@ -0,0 +1 @@
+book

outputs.nix

@@ -18,6 +18,35 @@ in (utils.lib.eachSystem (builtins.filter filter_system utils.lib.defaultSystems
     devShells.default = pkgs.callPackage ./shell.nix {
       inherit (sops-nix.packages."${pkgs.system}") sops-import-keys-hook ssh-to-pgp sops-init-gpg-key;
     };
+
+    packages = {
+      docs = pkgs.stdenv.mkDerivation {
+        name = "malobeo-docs";
+        phases = [ "buildPhase" ];
+        buildInputs = [ pkgs.mdbook ];
+      
+        inputs = pkgs.lib.sourceFilesBySuffices ./doc/. [ ".md" ".toml" ];
+      
+        buildPhase = ''
+          dest=$out/share/doc
+          mkdir -p $dest
+          cp -r --no-preserve=all $inputs/* ./
+          mdbook build
+          ls
+          cp -r ./book/* $dest
+        '';
+      };
+    };
+
+    apps = {
+      docs = {
+        type = "app";
+        program = builtins.toString (pkgs.writeScript "docs" ''
+          ${pkgs.mdbook}/bin/mdbook serve --open ./doc
+        '');
+      };
+    };
+
   })) // rec {
     nixosConfigurations = import ./machines/configuration.nix (inputs // {
       inherit inputs;