updating DIRECTORY.md

Author: CedricAnover

DIRECTORY.md

@@ -524,6 +524,7 @@
   * Tests
     * [Test Min Spanning Tree Kruskal](graphs/tests/test_min_spanning_tree_kruskal.py)
     * [Test Min Spanning Tree Prim](graphs/tests/test_min_spanning_tree_prim.py)
+  * [Travelling Salesman Problem](graphs/travelling_salesman_problem.py)
 
 ## Greedy Methods
   * [Best Time To Buy And Sell Stock](greedy_methods/best_time_to_buy_and_sell_stock.py)