Document how the shell *should* be built

Currently parcel doesn't support NODE_PATH, so this can't actually be
used. Need to push an issue upstream.

flake.nix

@@ -53,6 +53,19 @@
                 typescript-language-server
               ] ++ packages.nodeEnv.shell.buildInputs;
           };
+
+          # TODO: This would be the ideal. Sadly, parcel isn't smart
+          # enough to pull its plugins from $NODE_PATH.
+          #
+          #
+          # devShell = packages.nodeEnv.shell.override {
+          #   buildInputs = with prev; with nodePackages; [
+          #     node2nix
+
+          #     prettier
+          #     typescript-language-server
+          #   ];
+          # };
         };
       };
     };