Update bell_inequality.py (quantumlib#4998)

With the repetitions = 75, it is easy to get higher success rates than 85.3 if you re-run the code. It is therefore needed to mention that it is due to low repetitions and once increased to much higher values we get closer success rates to 85.3.

examples/bell_inequality.py

@@ -30,6 +30,10 @@
 -pi/4 followed by controlled-rotation by angle pi/2 in X-basis for
 Alice (Bob) based on input x (y).
 
+Note that the higher repetitions, the more accurate the maximum success
+probability (closer to 85.3%). Here, repetitions = 75 are chosen to follow
+the bit by bit logic.
+
 [1] https://en.wikipedia.org/wiki/Bell%27s_theorem
 [2] R. de Wolf. Quantum Computing: Lecture Notes
 (arXiv:1907.09415, Section 15.2)