update google_folder doc to include deletion_protection (GoogleCloudPlatform#13153)

Author: shuyama1

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

@@ -55,6 +55,8 @@ The following arguments are supported:
 * `parent` - (Required) The resource name of the parent Folder or Organization.
     Must be of the form `folders/{folder_id}` or `organizations/{org_id}`.
 
+* `deletion_protection` -  (Optional) Whether Terraform will be prevented from destroying or recreating the Folder. When the field is set to `true` or unset in Terraform state, a `terraform apply` or `terraform destroy` that would delete the folder will fail. When the field is set to `false`, deleting the folder is allowed. Default value is `true`.
+
 * `tags` - (Optional) A map of resource manager tags. Resource manager tag keys and values have the same definition as resource manager tags. Keys must be in the format tagKeys/{tag_key_id}, and values are in the format tagValues/456. The field is ignored when empty. The field is immutable and causes resource replacement when  mutated. This field is only set at create time and modifying this field after creation will trigger recreation. To apply tags to an existing resource, see the `google_tags_tag_value` resource.
 
 ## Attributes Reference