update WHATS_NEW

WHATS_NEW.md

@@ -28,7 +28,16 @@ VehicleRoutingAlgorithm vra = vraBuilder.build();
 
 <b> UNASSIGNED JOB LIST</b>
 
-- new feature: unassigned job list 
+A solution can now consists of assigned and unassigned jobs. There are various reasons for unassigned jobs, e.g. 
+demand exceeds available capacity, the job cannot be served within driver's operation time or the job is just too costly to 
+serve it with your own fleet.
+ 
+Note that jsprit uses "soft" approach to deal with unassigned jobs, i.e. each unassigned job will be penalyzed in the objective function 
+(see default objective https://github.com/jsprit/jsprit/blob/master/jsprit-core/src/main/java/jsprit/core/algorithm/VariablePlusFixedSolutionCostCalculatorFactory.java [line 55]). 
+If you omit penalyzing them, you probably end up with a solution consisting solely of unassigned jobs (the less the better in terms of total costs). 
+This, however, easily enables you to define objective functions that maximizes profits.
+
+Thus, if you already use your own custom objective function, you need to manually adapt it and add penalties for unassigned jobs.
 
 <b> STATEMANAGER </b>