Fix DAN Marketplace doc (#617)
Fix DAN Marketplace doc (#617)

* Add doc for DAN_Marketplace Adapter

* Fix format of DAN Marketplace doc file

* Fix DAN Marketplace doc

prebid/prebid.github.io,sonobi/prebid.github.io,prebid/prebid.github.io,sonobi/prebid.github.io,prebid/prebid.github.io,sonobi/prebid.github.io