added note on CleanupService

Change-Id: Ic23992804aa62171166efff5b9237a277a915177
Reviewed-on: http://gerrit.esdi-community.eu/3116
Tested-by: Jenkins <sitemple@igd.fraunhofer.de>
Reviewed-by: Simon Templer <simon.templer@igd.fraunhofer.de>