Add license information

[jamesmyatt]

Per https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license-and-license-files

Suggest #skip-changelog

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.83%. Comparing base (b28e9a3) to head (e46d757).
Report is 75 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #534      +/-   ##
==========================================
- Coverage   93.58%   92.83%   -0.76%     
==========================================
  Files         126      129       +3     
  Lines        6592     6766     +174     
==========================================
+ Hits         6169     6281     +112     
- Misses        423      485      +62     

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