Docs: Add a note to icinga check about failed reload detection
### icinga <a id="itl-icinga"></a>
Check command for the built-in `icinga` check. This check returns performance
-data for the current Icinga instance and optionally allows for minimum version checks.
+data for the current Icinga instance, reports as warning if the last reload failed and optionally allows for minimum version checks.
Custom variables passed as [command parameters](03-monitoring-basics.md#command-passing-parameters):