Missing exec_die event

Add also `exec_die` event.

Signed-off-by: Melroy van den Berg <melroy@melroy.org>

docs/reference/commandline/system_events.md

@@ -39,6 +39,7 @@ Docker containers report the following events:
 - `die`
 - `exec_create`
 - `exec_detach`
+- `exec_die`
 - `exec_start`
 - `export`
 - `health_status`