More complete settings for Pi-hole DNS setup.

roles/pihole/README.md

@@ -18,4 +18,15 @@ Then you can access `http://pi.hole/` in your browser and view the admin UI.
 
 ## DNS setup
 
-TODO.
+(This example is for macOS; other OSes and devices are similar.)
+
+  1. Open System Preferences.
+  2. Click on Network.
+  3. For whatever interface is at the top of the list and active for your connection (e.g. Wi-Fi or Ethernet), click the 'Advanced...' button.
+  4. Click the 'DNS' tab
+  5. Remove any existing entries under 'DNS Servers' (but note them in case if you want to switch back later).
+  6. Add the IP address of any of the worker nodes in the cluster.
+
+At this point, if you start browsing the web, then visit the admin UI, you should see requests are being blocked.
+
+If DNS requests are not resolving (e.g. most Internet things are not working), then revert the DNS settings to what they were previously.