doc: minor change to tox instructions

[math411]

Issue #, if available:

Description of changes:

Testing done:

Merge Checklist

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (fe5370c) to head (909a56b).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #231   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            7         7           
  Lines         1185      1185           
  Branches       286       286           
=========================================
  Hits          1185      1185           

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