improve explanation for factorial algorithm

[Vikash565-dot]

Added a clear explanation and example to help beginners understand the algorithm.
This improves readability and documentation quality.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.92%. Comparing base (08d8c6b) to head (8096f6d).

Additional details and impacted files

@@ Coverage Diff @@## master #1865 +/- ## ======================================= Coverage 85.91% 85.92% ======================================= Files 379 379 Lines 19778 19784 +6 Branches 3015 3014 -1 ======================================= + Hits 16993 16999 +6  Misses 2785 2785 

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[Vikash565-dot]

Let me know if any changes are required. Happy to update!