make fonts work in nix-shell

shell.nix

@@ -1,10 +1,20 @@
 with import <nixpkgs> {} ;
-let just = callPackage ./. {};
+let
+  just = callPackage ./. {};
 in just.overrideAttrs(o: {
   nativeBuildInputs = o.nativeBuildInputs ++ (with pkgs; [
     socat
     overmind
     entr
+  buildInputs = o.buildInputs ++ (with pkgs; [
+    gobject-introspection
+    gtk3
+    webkitgtk
   ]);
   JUST_HACKING = 1;
+
+  shellHook = with pkgs; ''
+    export XDG_DATA_DIRS=${gsettings-desktop-schemas}/share/gsettings-schemas/${gsettings-desktop-schemas.name}:${gtk3}/share/gsettings-schemas/${gtk3.name}:$XDG_DATA_DIRS;
+    export GIO_MODULE_DIR="${pkgs.glib-networking}/lib/gio/modules/";
+  '';
 })