[request] Document newTag output and how to consume it

[douglasg14b]

I was able to find this in the code by searching for >> $GITHUB_OUTPUT, but not many folks will know how to find this information.

Documenting the output and how to consume it would probably help a lot of people who need to perform their own commit & tag (ie. if they need to sync this version bump across different files before making a commit)

[phips28]

I would appreciate if you could do a PR for the docs 🙂