vl: add todo note about root container cleanup

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>

vl.c

@@ -4727,6 +4727,7 @@ int main(int argc, char **argv, char **envp)
     audio_cleanup();
     monitor_cleanup();
     qemu_chr_cleanup();
+    /* TODO: unref root container, check all devices are ok */
 
     return 0;
 }