Update README.md

Author: skillmaker-dev

README.md

@@ -38,6 +38,8 @@ or
  ### Sorting algorithms comparison: 
  ![SortBenchmark](https://user-images.githubusercontent.com/64654197/188233893-6ca26a71-7a30-4c21-95df-b25bb8719a6e.png)
 
+ #### Note :  BuiltIn Sorting algorithm uses an unstable version of QuickSort, and after .NET 4.5 it now uses Insertion sort for n<16, otherwise it starts with Quicksort and switches to Heapsort when the number of partitions (recursion depth?) exceeds 2 * Log^N. Called: Introsort, and that explains why it is the fastest.
+ 
  ### Searching algorithms comparison: 
  ![SearchingBenchmark](https://user-images.githubusercontent.com/64654197/188233962-b8a86341-007e-4e86-b607-52183f6acac2.png)