task(event-broker): Update readme for Profile Change Event

[dschom]

Because

• We've updated the event message schema for profileChangeUpdate events

This pull request

• Documents the changes

Checklist

Put an x in the boxes that apply

• [x] My commit is GPG signed.
• [ ] If applicable, I have modified or added tests which pass locally.
• [ ] I have added necessary documentation (if appropriate).
• [ ] I have verified that my changes render correctly in RTL (if appropriate).

[clouserw]

Dan and I discussed this. Closing this