Add derivative documentation

[ischoegl]

Changes proposed in this pull request

Add documentation of derivative calculation. Documentation is added to pre-existing Doxygen section.

If applicable, fill in the issue number this pull request is fixing

Closes Cantera/cantera-website#169

If applicable, provide an example illustrating new features this pull request is introducing

Checklist

• [x] The pull request includes a clear description of this code change
• [x] Commit messages have short titles and reference relevant issues
• [x] Build passes (scons build & scons test) and unit tests address code coverage
• [x] Style & formatting of contributed code follows contributing guidelines
• [x] The pull request is ready for review

[codecov[bot]]

Codecov Report

Merging #1563 (e08e824) into main (6ba497c) will not change coverage. The diff coverage is n/a.

:exclamation: Current head e08e824 differs from pull request most recent head 83c2766. Consider uploading reports for the commit 83c2766 to get more accurate results

@@           Coverage Diff           @@
##             main    #1563   +/-   ##
=======================================
  Coverage   70.45%   70.45%           
=======================================
  Files         379      379           
  Lines       59093    59093           
  Branches    21230    21230           
=======================================
  Hits        41636    41636           
  Misses      14376    14376           
  Partials     3081     3081           

Files Changed	Coverage Δ
include/cantera/kinetics/Kinetics.h	32.66% <ø> (ø)
include/cantera/kinetics/ReactionRate.h	78.87% <ø> (ø)

... and 10 files with indirect coverage changes

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[ischoegl]

Rebased and ready for review. BibTeX sort moved to #1567.

[ischoegl]

Thanks for the review comments. I took care of everything except for what I believe is a CSS styling issue?