docs: update DIRECTORY.md (#2899)

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DIRECTORY.md

@@ -41,6 +41,7 @@
 
 ## Cpu Scheduling Algorithms
   * [Fcfs Scheduling](https://github.com/TheAlgorithms/C-Plus-Plus/blob/HEAD/cpu_scheduling_algorithms/fcfs_scheduling.cpp)
+  * [Non Preemptive Sjf Scheduling](https://github.com/TheAlgorithms/C-Plus-Plus/blob/HEAD/cpu_scheduling_algorithms/non_preemptive_sjf_scheduling.cpp)
 
 ## Data Structures
   * [Avltree](https://github.com/TheAlgorithms/C-Plus-Plus/blob/HEAD/data_structures/avltree.cpp)