added explanatory comment

Author: KA7E

vpr/src/pack/re_cluster_util.h

@@ -100,6 +100,7 @@ bool start_new_cluster_for_mol(t_pack_molecule* molecule,
  * @param clustering_data: A data structure containing helper data for the clustering process
  *                          (is updated if this function is called during packing, especially intra_lb_routing data member).
  * @param router_data: returns the intra logic block router data.
+ * @param enable_pin_feasibility_filter: do a pin couting based legality check (before or in place of intra-cluster routing check).
  */
 bool pack_mol_in_existing_cluster(t_pack_molecule* molecule,
                                   int molecule_size,