Feature/180 add faqs

[fossell]

Adding a FAQ section to the UG. This closes #180.

• [x] Do these changes modify the system output in any way? [No]
  If yes, please describe:
  

Pull Request Testing

• [x] Describe testing already performed for these changes:
  Built the documentation with RTDs here and confirmed new section is working and formatted properly.

• [ ] Recommend testing for the reviewer(s) to perform, including the location of input datasets, and any additional instructions:
  View the RTD build here and comment on any issues or changes.

• [x] Do these changes include sufficient documentation updates, ensuring that no errors or warnings exist in the build of the documentation? [Yes]

• [x] Do these changes include sufficient testing updates? [N/A]

• [x] Will this PR result in changes to the test suite? [No]
  If yes, describe the new output and/or changes to the existing output:
  

• [ ] Please complete this pull request review by [6/26/23].
  

Pull Request Checklist

• [x] Review the source issue metadata (labels, project, and milestone).
• [x] Complete the PR definition above.
• [x] Ensure the PR title matches the feature or bugfix branch name.
• [x] Define the PR metadata, as permissions allow. Select: Reviewer(s) Select: Project Select: Milestone as the version that will include these changes Select: Development to link to the original development issue.
• [ ] After the PR is approved, merge your changes. If permissions do not allow this, request that the reviewer do the merge.
• [ ] Close the linked issue and delete your feature or bugfix branch from GitHub.

[fossell]

The documentation test is likely failing because sphinx-design needs to be added to the documentation.yaml file for the test. Will push a commit to add it.

[fossell]

@hahnd - Can you please approve if this is now good to go with the units mods? Thanks!