document how to make Electron apps use wayland natively

modules/universal/env/default.nix

@@ -13,6 +13,10 @@
     EDITOR = "vim";
     # git claims it should use EDITOR, but it doesn't!
     GIT_EDITOR = "vim";
+    # Electron apps should use native wayland backend:
+    #   https://nixos.wiki/wiki/Slack#Wayland
+    # Discord under sway crashes with this.
+    # NIXOS_OZONE_WL = "1";
   };
 }