updating DIRECTORY.md

Author: github-actions

DIRECTORY.md

@@ -176,6 +176,7 @@
       * [Test Singly Linked List Pairwise Swap](https://github.com/BrianLusina/PythonSnips/blob/master/datastructures/linked_lists/singly_linked_list/test_singly_linked_list_pairwise_swap.py)
       * [Test Singly Linked List Remove Duplicates](https://github.com/BrianLusina/PythonSnips/blob/master/datastructures/linked_lists/singly_linked_list/test_singly_linked_list_remove_duplicates.py)
       * [Test Singly Linked List Rotate](https://github.com/BrianLusina/PythonSnips/blob/master/datastructures/linked_lists/singly_linked_list/test_singly_linked_list_rotate.py)
+      * [Test Singly Linked Move Tail To Head](https://github.com/BrianLusina/PythonSnips/blob/master/datastructures/linked_lists/singly_linked_list/test_singly_linked_move_tail_to_head.py)
       * [Test Singly Linked Palindrome](https://github.com/BrianLusina/PythonSnips/blob/master/datastructures/linked_lists/singly_linked_list/test_singly_linked_palindrome.py)
   * Lists
     * Bus Stops