docs(cloudflare): set ttl annotation for cloudflare proxied entries to 1

Author: jerome-lecorvaisier

docs/tutorials/cloudflare.md

@@ -165,6 +165,7 @@ of the DNS zone (e.g. 'www.example.com').
 
 By setting the TTL annotation on the service, you have to pass a valid TTL, which must be 120 or above.
 This annotation is optional, if you won't set it, it will be 1 (automatic) which is 300.
+For Cloudflare proxied entries, set the TTL annotation to 1 (automatic), or do not set it.
 
 ExternalDNS uses this annotation to determine what services should be registered with DNS.  Removing the annotation
 will cause ExternalDNS to remove the corresponding DNS records.