add doi to README and citation.cff

[yiwen-h]

Closes #172

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.77%. Comparing base (4726aed) to head (1e34b5e).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #174   +/-   ##
=======================================
  Coverage   84.77%   84.77%           
=======================================
  Files           9        9           
  Lines         703      703           
  Branches       78       78           
=======================================
  Hits          596      596           
  Misses         98       98           
  Partials        9        9           

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