Add doctoc to automatically generate TOCs

[lucacome]

Proposed changes

The README is very long and it's hard to find things without a TOC.
The Contributing Guidelines had new sections that were never added to the TOC.

With doctoc we can keep the TOCs up to date automatically.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING guide
• I have proven my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have ensured the README is up to date
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch on my own fork