[datadog_monitor_notification_rule] Update docs with preview description (#3003)

* Update docs with preview description

* update description, capitalize preview

Author: shaneyuandd

datadog/fwprovider/resource_datadog_monitor_notification_rule.go

@@ -64,7 +64,7 @@ func (r *MonitorNotificationRuleResource) Metadata(_ context.Context, request re
 
 func (r *MonitorNotificationRuleResource) Schema(_ context.Context, _ resource.SchemaRequest, response *resource.SchemaResponse) {
 	response.Schema = schema.Schema{
-		Description: "Provides a Datadog MonitorNotificationRule resource.",
+		Description: "Provides a Datadog MonitorNotificationRule resource. *Note: This resource is in Preview. [Request access](https://www.datadoghq.com/product-preview/monitor-notification-rules/).*",
 		Attributes: map[string]schema.Attribute{
 			"id": utils.ResourceIDAttribute(),
 			"name": schema.StringAttribute{

docs/resources/monitor_notification_rule.md

@@ -3,12 +3,12 @@
 page_title: "datadog_monitor_notification_rule Resource - terraform-provider-datadog"
 subcategory: ""
 description: |-
-  Provides a Datadog MonitorNotificationRule resource.
+  Provides a Datadog MonitorNotificationRule resource. Note: This resource is in Preview. Request access https://www.datadoghq.com/product-preview/monitor-notification-rules/.
 ---
 
 # datadog_monitor_notification_rule (Resource)
 
-Provides a Datadog MonitorNotificationRule resource.
+Provides a Datadog MonitorNotificationRule resource. *Note: This resource is in Preview. [Request access](https://www.datadoghq.com/product-preview/monitor-notification-rules/).*
 
 ## Example Usage