update system

os/system/virtualisation.nix

@@ -1,3 +1,12 @@
 { pkgs, ... }: {
-  virtualisation.docker.enable = true;
+  virtualisation = {
+    docker.enable = true;
+    # following configuration is added only when building VM with build-vm
+    vmVariant = {
+      virtualisation = {
+        memorySize = 2048;
+        cores = 2;
+      };
+    };
+  };
 }