brand lift measurement: use cases and explainer

Hello everyone,

Following up on the brief discussion of brand lift measurement we had on
the call several weeks ago, I've just submitted a pull request adding a use
case for "brand lift" measurement to the "support for use cases" document.

The pull request also contains several documents/additions that describe:

* what brand advertising is, and how it differs from conversion-focused
"direct response" advertising
* why brand advertising is important to the economic health of the open web
* what "brand lift" measurement is, and why it's an essential part of
keeping brand advertising dollars flowing into the web
* how brand lift measurement is currently conducted
* how the deprecation of 3rd party cookies will break all current methods
for reliably measuring brand lift on the web

https://github.com/w3c/web-advertising/pull/58

I'd welcome reviews/input/feedback from anyone who is interested in brand
advertising, brand lift measurement, or in APIs to support their transition
to a more private web.

Wendy, I'd also appreciate if we could put an item on Tuesday's agenda to
discuss (or at least introduce) these materials. (I believe we may already
have an overflow item from last week to discuss new use cases, and if so
this would fit in well there.)

Thanks kindly, and I hope everyone has a great upcoming weekend!

-George London
Director of Engineering <https://www.linkedin.com/in/georgelondon/> @
Survata <http://survata.com>