[DNS] Update setup.mdx

Author: ngayerie

src/content/docs/dns/dns-firewall/setup.mdx

@@ -41,6 +41,8 @@ Prior to setting up DNS Firewall, you need:
 
 If you forget to save your new IP addresses, find your cluster and click **IP Addresses**.
 
+If you delete your cluster, the assigned set of IPs will be lost: if you recreate the cluster you will get a different set of IPs.
+
 :::
 
 </TabItem> <TabItem label="API">