Ad Topic Hints proposal

Thank you everyone who participated in the last discussion on "Ad Topic Hints" a few weeks ago.

We have written up a first draft of the proposal which you can find here: https://github.com/privacycg/ad-topic-hints

I would love to discuss this in our upcoming call on Thursday. No "issues" yet - but please feel free to file them here: https://github.com/privacycg/ad-topic-hints/issues

--Ben