[Mahjong] Add some comments for development

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (cb470fb) 88.09% compared to head (cbb4728) 88.09%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1123 +/- ## ======================================= Coverage 88.09% 88.09% ======================================= Files 60 60 Lines 5922 5924 +2 ======================================= + Hits 5217 5219 +2 Misses 705 705 ```

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