Documentation pass

[timspainNERSC]

As the code stabilizes and more people than just me need to work with and maintain it, the in-line documentation should be improved. Taking a fresh pass over the documentation before it falls to far in to the Memory Hole could be a productive use of Julferie time.

[a-smith-github]

During this work, can we also capture the new install instructions to reflect those in clang-compile-tests.yml for mac (and probably linux too)? Particularly thinking of Catch2 and include install for eigen, netcdf-cxx.