add writeable nix-store

hosts/leoncloud/default.nix

@@ -13,6 +13,16 @@ in
     mem = 1024;
   };
 
+  writableStoreOverlay = "/nix/.rw-store";
+
+  volumes = [ {
+    image = "nix-store-overlay.img";
+    mountPoint = config.microvm.writableStoreOverlay;
+    size = 2048;
+  } ];
+
+
+
   c3d2.deployment = {
     server = "server9";
     mounts = [ "etc" "home" "var"];