describe truncate feature about advanced audit

content/en/docs/tasks/debug-application-cluster/audit.md

@@ -191,6 +191,17 @@ and in the logs to monitor the state of the auditing subsystem.
 - `apiserver_audit_error_total` metric contains the total number of events dropped due to an error
   during exporting.
 
+### truncate
+
+Both log and webhook backends support batching. As an example, the following is the list of flags
+available for the log backend:
+
+ - `audit-log-truncate-enabled` whether event and batch truncating is enabled.
+ - `audit-log-truncate-max-batch-size` maximum size of the batch sent to the underlying backend.
+ - `audit-log-truncate-max-event-size` maximum size of the audit event sent to the underlying backend.
+
+By default truncate is disabled in both `webhook` and `log`.
+
 ## Multi-cluster setup
 
 If you're extending the Kubernetes API with the [aggregation layer][kube-aggregator], you can also