nix-flatpak to get declarative flatpaks

flake.nix

@@ -12,9 +12,11 @@
       url = "gitlab:rycee/nur-expressions?dir=pkgs/firefox-addons";
       inputs.nixpkgs.follows = "nixpkgs";
     };
+
+    nix-flatpak.url = "github:gmodena/nix-flatpak/?ref=latest";
   };
 
-  outputs = { nixpkgs, ... } @ inputs:
+  outputs = { self, nixpkgs, nix-flatpak, ... } @ inputs:
     let
       system = "x86_64-linux";
     in
@@ -25,6 +27,7 @@
         specialArgs = { inherit inputs system; };
         modules = [
           ./configuration.nix
+	  nix-flatpak.nixosModules.nix-flatpak
         ];
       };