Replace links by DirectoryListing and add note on external CDN

Author: RebeccaTamachiro

src/content/docs/cloudflare-for-platforms/cloudflare-for-saas/domain-support/hostname-validation/index.mdx

@@ -6,14 +6,12 @@ sidebar:
 
 ---
 
+import { DirectoryListing } from "~/components";
+
 Before Cloudflare can proxy traffic through a custom hostname, we need to verify your customer's ownership of that hostname.
 
 :::note
-
-
 If a custom hostname is already on Cloudflare, using the [pre-validation methods](/cloudflare-for-platforms/cloudflare-for-saas/domain-support/hostname-validation/pre-validation/) will not shift the traffic to the SaaS zone. That will only happen once the [DNS target](/cloudflare-for-platforms/cloudflare-for-saas/start/getting-started/#3-have-customer-create-cname-record) of the custom hostnames changes to point to the SaaS zone.
-
-
 :::
 
 ## Options
@@ -22,7 +20,10 @@ If minimizing downtime is more important to you, refer to our [pre-validation me
 
 If ease of use for your customers is more important, review our [real-time validation methods](/cloudflare-for-platforms/cloudflare-for-saas/domain-support/hostname-validation/realtime-validation/).
 
-## Other resources
+## Limitations
+
+Custom hostnames using another CDN are not compatible with Cloudflare for SaaS. Since Cloudflare must be able to validate your customer's ownership of the hostname you add, if their usage of another CDN obfuscates their DNS records, hostname validation will fail.
+
+## Related resources
 
-* [Hostname validation statuses](/cloudflare-for-platforms/cloudflare-for-saas/domain-support/hostname-validation/validation-status/)
-* [Error codes](/cloudflare-for-platforms/cloudflare-for-saas/domain-support/hostname-validation/error-codes/)
+<DirectoryListing />