Documentation updates

• Adding a nomenclature reference
• Adding a table of contents with links to all docs, in readme.md
• Moving images used in docs to docs/assets subfolder to make docs/ folder easier to navigate

How to Test

(Please describe how to exercise these changes in the application)

Screenshots

(If visual changes are introduced, show what they look like)

Post-Merge Checklist

• Create follow-up issues for anything left over for another merge request
  • If any technical debt is introduced, assign these follow-up issues to the MR submitter