Update rediscloud_subscription.md (#311)

* Update rediscloud_subscription.md

As we are not supporting it for our hosted AWS solution, it may and confuse customers.

Author: noham14

docs/resources/rediscloud_subscription.md

@@ -120,7 +120,7 @@ within the hosting account.
 * `preferred_availability_zones` - (Required) Availability zones deployment preferences (for the selected provider & region).
 
 ~> **Note:** The preferred_availability_zones parameter is required for Terraform, but is optional within the Redis Enterprise Cloud UI. 
-This difference in behaviour is to guarantee that a plan after an apply does not generate differences.
+This difference in behaviour is to guarantee that a plan after an apply does not generate differences.  In AWS Redis internal cloud account, please set an empty list.
 
 ### Timeouts