Discuss optional keys (#2738)
Discuss optional keys (#2738)

* Update publisher-api-reference.md

* wordsmithing

good improvement. made a few updates.

Co-authored-by: bretg <9df09da23577b88db5b6b8911d0635d4f870e78e@gmail.com>
prebid/prebid.github.io,prebid/prebid.github.io,prebid/prebid.github.io