add comment to link to the new (yet to implement) algorithm

VadereSimulator/src/org/vadere/simulator/projects/dataprocessing/processor/PedestrianDensityCountingProcessor.java

@@ -7,7 +7,8 @@ import org.vadere.state.attributes.processor.AttributesProcessor;
 
 /**
  * @author Mario Teixeira Parente
- *
+ * This processor counts the density for each pedestrian (density per pedestrian id) by counting pedestrians that are
+ * in 'radius'. To count pedestrians in a measurement area look at AreaDensityCountingProcessor.
  */
 @DataProcessorClass()
 public class PedestrianDensityCountingProcessor extends PedestrianDensityProcessor {