nix: added 'website' command to build website correctly in dev shell

flake.nix

@@ -66,6 +66,13 @@
             '';
           };
           commands = [
+            {
+              name = "website";
+              command = ''
+                nix build '.?submodules=1#website'
+              '';
+              help = "Build the website with submodules included and export to the result folder.";
+            }
             {
               name = "build";
               # dev dependencies include "hugo-extended", which fails to
@@ -96,4 +103,4 @@
         });
       }
     );
-}
+}