Add hash to headers

[benolayinka]

Summary

Adds a hash on hover to section headers

Screenshots

Checklist

• [x] Scope: The referenced issue is addressed, there are no unrelated changes.
• [x] Run Locally: Verified that the docs build using make server, posted screenshots, verified external links.
• [ ] Style Guidelines: Documentation obeys style guidelines in CONTRIBUTING.
• [x] Commits: Commit messages follow guidelines in CONTRIBUTING, there are no fixup commits left.