[vpr][util] add comment for get_cluster_block_pins

Author: amin1377

vpr/src/util/vpr_utils.h

@@ -328,7 +328,12 @@ std::vector<int> get_cluster_netlist_intra_tile_pins_at_loc(const t_physical_til
                                                             const vtr::vector<ClusterBlockId, t_cluster_pin_chain>& pin_chains,
                                                             const vtr::vector<ClusterBlockId, std::unordered_set<int>>& pin_chains_num,
                                                             t_physical_tile_type_ptr physical_type);
-
+/**
+ * @brief Returns the list of pins (both cluster-level and intra-cluster-level) of the given cluster block.
+ * @param physical_tile The physical tile type that the cluster block is mapped to.
+ * @param cluster_blk_id The cluster block ID.
+ * @param abs_cap The absolute capacity number of the sub-tile that the cluster block is mapped to.
+ */
 std::vector<int> get_cluster_block_pins(t_physical_tile_type_ptr physical_tile,
                                         ClusterBlockId cluster_blk_id,
                                         int abs_cap);