Bright Mountain Media: Update bidder code (#2857)

* Add Bright Mountain Media Adapter website doc

* Update brightmountainmedia.md

adding quotes on string example and the new 'pbjs: true' header, which will soon be needed

* Bright Mountain Media: Change bidder code

Co-authored-by: bretg <bgorsline@gmail.com>

dev-docs/bidders/brightmountainmedia.md

@@ -3,7 +3,7 @@ layout: bidder
 title: Bright Mountain Media
 description: Prebid Bright Mountain Media Bidder Adapter
 pbjs: true
-biddercode: brightmountainmedia
+biddercode: bmtm
 media_types: banner
 ---