trying to get niri to show up in dm

modules/niri/default.nix

@@ -1,5 +1,21 @@
-{ pkgs, ... }: {
-  environment.systemPackages = [
-    (pkgs.callPackage ./niri {})
+{ pkgs, ... }: 
+{
+  services.xserver.displayManager.sessionPackages = [
+    ((pkgs.callPackage ./niri {}).overrideAttrs (prevAttrs: rec {
+      postInstall =
+      let
+        niriSession = ''
+          [Desktop Entry]
+          Name=niri
+          Comment=Scrolling wayland compositor
+          Exec=niri
+          Type=Application
+          '';
+      in ''
+          mkdir -p $out/share/wayland-sessions
+          echo "${niriSession}" > $out/share/wayland-sessions/niri.desktop
+        '';
+      passthru.providedSessions = [ "niri" ];
+    }))
   ];
 }