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

[ryan-roemer]

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.