Add reference link for running median algorithm

Author: Bharatgwl

data_structures/heap/median_in_a_stream.py

@@ -64,7 +64,10 @@ def median_in_a_stream(numbers: List[int]) -> List[int]:
     Find the median after each insertion in a stream of integers.
 
     Uses two heaps and follows the classic running median logic.
-
+    
+    Reference:
+    https://en.wikipedia.org/wiki/Median#Running_median
+    
     Args:
         numbers: List of integers