Fix #42, Resolve usersguide issues with doxygen 1.8.17

[skliper]

Checklist (Please check before submitting)

• I reviewed the Contributing Guide.
• I signed and emailed the appropriate Contributor License Agreement to GSFC-SoftwareRelease@mail.nasa.gov and copied cfs-program@lists.nasa.gov.

Describe the contribution

• Fix Resolve issues building users guide with Ubuntu 20.04/Doxygen 1.8.17 #42

Testing performed
Build doc with Ubuntu 20.04

Expected behavior changes
Successful doc build

System(s) tested on

• Hardware: i5/Docker
• OS: Ubuntu 20.04
• Versions: Bundle main + this commit

Additional context
None

Third party code
None

Contributor Info - All information REQUIRED for consideration of pull request
Jacob Hageman - NASA/GSFC