nixos/plasma5: add xdg-user-dirs to create user directories

nixos/modules/services/x11/desktop-managers/plasma5.nix

@@ -163,6 +163,8 @@ in
 
           libsForQt56.phonon-backend-gstreamer
           libsForQt5.phonon-backend-gstreamer
+
+          xdg-user-dirs # Update user dirs as described in https://freedesktop.org/wiki/Software/xdg-user-dirs/
         ]
 
         ++ lib.optionals cfg.enableQt4Support [ pkgs.phonon-backend-gstreamer ]
@@ -175,9 +177,9 @@ in
         ++ lib.optional config.services.colord.enable colord-kde
         ++ lib.optionals config.services.samba.enable [ kdenetwork-filesharing pkgs.samba ];
 
-      environment.pathsToLink = [ 
+      environment.pathsToLink = [
         # FIXME: modules should link subdirs of `/share` rather than relying on this
-        "/share" 
+        "/share"
       ];
 
       environment.etc = singleton {