Update README.md

ch02/README.md

@@ -369,3 +369,13 @@ L.I. holds.
 ```cpp
 {2,1}, {3,1}, {8,1}, {6,1}, {8,6}
 ```
+ * set {n, n-1, n-2, ...,2, 1}, i.e. numbers in descending order has most inversions.
+ * As shown below, the expression `A[i] > key` is in essence checking for an inversion. So a function can be made to describe the relationship between the running time and number of inversions:
+```cpp
+  T(n) = theta(n * number_of_inversions + n)
+```
+
+```cpp
+//from Insertion-Sort
+5     while i > 0 and A[i] > key
+```