updating DIRECTORY.md

Author: github-actions

DIRECTORY.md

@@ -233,6 +233,7 @@
     * [Merge Two Lists](data_structures/linked_list/merge_two_lists.py)
     * [Middle Element Of Linked List](data_structures/linked_list/middle_element_of_linked_list.py)
     * [Print Reverse](data_structures/linked_list/print_reverse.py)
+    * [Reverse K Group](data_structures/linked_list/reverse_k_group.py)
     * [Rotate To The Right](data_structures/linked_list/rotate_to_the_right.py)
     * [Singly Linked List](data_structures/linked_list/singly_linked_list.py)
     * [Skip List](data_structures/linked_list/skip_list.py)