[LMS-1452] update properties

SVN: 15250

datastore_server/dist/etc/service.properties

@@ -175,6 +175,7 @@ main-thread.incoming-data-completeness-condition = marker-file
 # Mandatory properties for each <plugin> include: 
 #   <plugin>.class - Fully qualified plugin class name
 #   <plugin>.interval - The time between plugin executions (in seconds)
+# Optional properties for each <plugin> include:
 #   <plugin>.start - Time of the first execution (hh:mm)
 #maintenance-plugins =