docs/r/sns_topic_subscription: Add note to docs

website/docs/r/sns_topic_subscription.html.markdown

@@ -18,7 +18,7 @@ Provides a resource for subscribing to SNS topics. Requires that an SNS topic ex
 
 ~> **NOTE:** If an SNS topic and SQS queue are in different AWS accounts and different AWS regions, the subscription needs to be initiated from the account with the SQS queue but in the region of the SNS topic.
 
-~> **NOTE:** You cannot unsubscribe to a subscription that is pending confirmation. If you use `email`, `email-json`, or `http`/`https` (without auto-confirmation enabled), until the subscription is confirmed (e.g., outside of Terraform), AWS does not allow Terraform to delete / unsubscribe the subscription. If you `destroy` an unconfirmed subscription, Terraform will remove the subscription from its state but the subscription still exist in AWS.
+~> **NOTE:** You cannot unsubscribe to a subscription that is pending confirmation. If you use `email`, `email-json`, or `http`/`https` (without auto-confirmation enabled), until the subscription is confirmed (e.g., outside of Terraform), AWS does not allow Terraform to delete / unsubscribe the subscription. If you `destroy` an unconfirmed subscription, Terraform will remove the subscription from its state but the subscription still exist in AWS. However, if you delete an SNS topic, SNS [deletes all the subscriptions](https://docs.aws.amazon.com/sns/latest/dg/sns-delete-subscription-topic.html) associated with the topic.
 
 ## Example Usage