Add contributing section to readme

[codecov[bot]]

Codecov Report

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

Project coverage is 75.89%. Comparing base (61f172c) to head (c404e2e).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #134 +/- ## ======================================= Coverage 75.89% 75.89% ======================================= Files 13 13 Lines 1788 1788 ======================================= Hits 1357 1357 Misses 431 431 ```

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