Clarify definition of pE vs. redox potential in documentation

[ugognw]

Summary

Major changes:

• feature: closes Docs: clarify definition of pE vs. redox potential in documentation #230

Checklist

• Google format doc strings added.
• Code linted with ruff. (For guidance in fixing rule violates, see rule list)
• Type annotations included. Check with mypy.
• Tests added for new features/fixes.
• I have run the tests locally and they passed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.79%. Comparing base (b361c6a) to head (f3ebfb1).
Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #253   +/-   ##
=======================================
  Coverage   81.79%   81.79%           
=======================================
  Files           9        9           
  Lines        1494     1494           
  Branches      257      257           
=======================================
  Hits         1222     1222           
  Misses        226      226           
  Partials       46       46           

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[rkingsbury]

Thank you @ugognw !