Add full usage demonstration for BillSplitterMDS

[quandothoang]

Added a full usage demonstration for the BillSplitterMDS package, including steps for preparing data, loading and validating, calculating payments, and determining transfers needed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.80%. Comparing base (cd0154b) to head (f81f9ca).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #66   +/-   ##
=======================================
  Coverage   98.80%   98.80%           
=======================================
  Files           5        5           
  Lines          84       84           
=======================================
  Hits           83       83           
  Misses          1        1           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[mayitoxix]

Thanks for taking care of this @quandothoang