readme: condescending note about manual niri config

README.md

@@ -150,6 +150,24 @@ programs.nova-shell.systemd = {
 };
 ```
 
+### Niri overview backdrop
+
+If you use the Home Manager module like a civilized person, the required niri
+layer rule is added automatically. If you insist on managing your niri config
+by hand — because declarative configuration is apparently too convenient — add
+this to your `config.kdl`:
+
+```kdl
+layer-rule {
+    match namespace="^nova-overview-backdrop$"
+    place-within-backdrop true
+}
+```
+
+Without this, the overview backdrop widgets won't be visible between workspace
+rows. The bar will still work, you'll just miss out on the pretty parts, which
+is arguably what you deserve for not using Nix properly.
+
 ## Contributing
 
 Sure, why not. It can't get much worse, and the GPL requires you to share