Auto create blank snapshot using disko

hosts/nixos/calypso/filesystems/partitions.nix

@@ -33,14 +33,10 @@
               type = "btrfs";
               extraArgs = [ "-f" ];
 
-              # TODO: how do we do this properly???
-              postCreateHook = ''
-                # We then take an empty *readonly* snapshot of the root subvolume,
-                # which we'll eventually rollback to on every boot.
-                # btrfs subvolume snapshot -r /root /blank
-              '';
-
               subvolumes = {
+                # {{{ /blank
+                "/blank" = { };
+                # }}}
                 # {{{ /root
                 "/root" = {
                   mountpoint = "/";