Add example reference zone API call

Author: RebeccaTamachiro

src/content/docs/dns/internal-dns/get-started.mdx

@@ -58,7 +58,17 @@ Although there are some steps that can be achieved on the dashboard, currently t
 <Example>
 In the following example, internal zone A (ID `8a904aeb565c42cfa207d98f6edea2f3`) is referencing internal zone B (ID `8e64c6fb4b514f3faf64de81efc11e51`).
 
-TBD > add full API call example using IDs mentioned above
+```bash
+curl --request PATCH \
+https://api.cloudflare.com/client/v4/zones/8a904aeb565c42cfa207d98f6edea2f3/dns_settings \
+--header "Authorization: Bearer $CLOUDFLARE_API_TOKEN" \
+--header "Content-Type: application/json" \
+--data '{
+    "internal_dns": {
+        "reference_zone_id": "8e64c6fb4b514f3faf64de81efc11e51D"
+    }
+  }'
+```
 </ Example>
 
 ## 2. Link your internal zone to a view