Fix any mkdocs site page content issues

[fyliu]

Dependency

• 166

Overview

Some parts of the newly-converted documentation might not look right in mkdocs. We need to fix the existing problems.

Action Items

• [x] look for issues in the documentation (things that could be converted into mkdocs formatting, like special notes)
• [x] fix the issues
• [x] document how to write documentation the mkdocs way to avoid the issues

After Merge

• [ ] Release #184 from the ice box
• [ ] Check #185 for completion

Resources/Instructions

• The block quotes in the add model guide will likely need updating. Maybe there are other issues.
• Reference the old sphinx docs for peopledepot for what can/should be done.
  • The contributing page there has examples of things that benefit from having tabbed content and admonitions.

[fyliu]

• See #232 for discussion on needing content tabs support in mdformat-mkdocs in order to autoformat the markdown constructs being used here.