Update heap_sort.c

Added time complexities of functions used.

Author: Shwetik

sorting/heap_sort.c

@@ -1,3 +1,8 @@
+/**
+ * max_heapify takes O(logn).
+ * build_maxheap takes O(n).
+ * heapsort takes O(nlogn) since it requires above mentioned functions.
+ */
 #include <stdio.h>
 
 void max_heapify(int *a, int i, int n);