[DNS] Add link to subdomain setups from how-to page (#19906)

* Update subdomains-outside-cloudflare.mdx

adding a note for the reverse; subdomain setups after customers told they were unable to find it
- kai

* Fix typo and update link to more specific page

---------

Co-authored-by: Rebecca Tamachiro <[email protected]>

Author: kbitr

src/content/docs/dns/manage-dns-records/how-to/subdomains-outside-cloudflare.mdx

@@ -29,7 +29,7 @@ Cloudflare's CDN and security services are not applied to delegated subdomains.
 
 ***
 
-## Delegate a subdomain
+## Delegate a subdomain (outgoing)
 
 To delegate a subdomain such as *internal.example.com*, tell DNS resolvers where to find the zone file:
 
@@ -44,3 +44,7 @@ To delegate a subdomain such as *internal.example.com*, tell DNS resolvers wher
    The `A` records for the subdomain are only required as glue records for nameservers that are located in the subdomain of the current zone that is being delegated.
    :::
 5. (Optional) If the delegated nameserver has DNSSEC enabled, [add the `DS` record](/dns/dnssec/#1-activate-dnssec-in-cloudflare) in Cloudflare.
+
+## Delegate a subdomain (incoming)
+
+To delegate a subdomain from an external DNS provider to Cloudflare, refer to [subdomain setups](/dns/zone-setups/subdomain-setup/setup/).