trace-pkg: Add back support for build/build:toc

In `trace-pkg/package.json` we presently have two build tasks to update the README.md TOC. Work:

- [ ] Decide if we want this in trace-pkg
- [ ] Decide if we want to add to trace-deps too
- [ ] Add a git dirty check to make sure we don't have missed additions?
- [ ] Remove `TODO` messages in `trace-pkg/package.json` and implement decisions from above.

Start by reading trace-pkg/package.json and the existing build tasks that update README.md's TOC. Resolve whether the support belongs in trace-pkg and trace-deps, then determine the intended git-dirty check. Done means the decisions are implemented and the TODO messages are removed from trace-pkg/package.json.

Written by the indexing model from the issue text.