Update 03_operators.md

[Tasnimsomo]

Summary

Fixed a small issue in the comparison operator examples. The original text described the not in operator but didn’t include a working example or had a typo.

Changes Made

• Added missing example for not in comparison
• Corrected description from (x in y) to (x not in y)

Why This Change Was Needed

This makes the tutorial more accurate and consistent. The previous version could confuse beginners since the explanation didn’t match the examples.

Example Output

print('B not in Asabeneh:', 'B' not in 'Asabeneh')  # True