Add drop appimage.

nodes/hosts/common/programs/drop.nix

@@ -0,0 +1,11 @@
+{ pkgs, lib, inputs, ... }:
+
+let 
+  dropApp = import ../../../appimages/drop.nix { inherit pkgs; };
+in
+{
+  # ...
+  environment.systemPackages = [
+    pkgs.dropApp
+  ];
+}