bigtable: add automated backups documentation to bigtable table (Goog…

…leCloudPlatform#11162)

mmv1/third_party/terraform/website/docs/r/bigtable_table.html.markdown

@@ -52,6 +52,11 @@ resource "google_bigtable_table" "table" {
   }
 
   change_stream_retention = "24h0m0s"
+
+  automated_backup_policy {
+    retention_period = "72h0m0s"
+    frequency = "24h0m0s"
+  }
 }
 ```
 
@@ -76,6 +81,8 @@ to delete/recreate the entire `google_bigtable_table` resource.
 
 * `change_stream_retention` - (Optional) Duration to retain change stream data for the table. Set to 0 to disable. Must be between 1 and 7 days.
 
+* `automated_backup_policy` - (Optional) Defines an automated backup policy for a table, specified by Retention Period and Frequency. To disable, set both Retention Period and Frequency to 0.
+
 -----
 
 `column_family` supports the following arguments: