snixembed: add waybar incompatbility warning

If snixembed is enabled and you try to use the waybar tray the two tools
conflict with eachother and often waybar's tray will not show any icons.
This adds a warning about it, as the problem can be difficult to
diagnose.

modules/services/snixembed.nix

@@ -7,6 +7,7 @@
 
 let
   cfg = config.services.snixembed;
+  waybarCfg = config.programs.waybar;
 in
 {
   meta.maintainers = [ lib.maintainers.DamienCassou ];
@@ -32,6 +33,10 @@ in
     assertions = [
       (lib.hm.assertions.assertPlatform "services.snixembed" pkgs lib.platforms.linux)
     ];
+    warnings = lib.optional waybarCfg.enable ''
+      snixembed and waybar should not be enabled at the same time.
+      You may experience inconsistent tray behavior as a result.
+    '';
 
     systemd.user.services.snixembed = {
       Install.WantedBy = [ "graphical-session.target" ];