New Adapter: Concert (#2033)

* Add documentation for concert bid adapter

* Add quotes around example value

dev-docs/bidders/concert.md

@@ -0,0 +1,17 @@
+---
+layout: bidder
+title: Concert
+description: Prebid Concert Bidder Adaptor
+hide: true
+biddercode: concert
+media_types: banner
+gdpr_supported: true
+usp_supported: true
+---
+
+### Bid Params
+
+{: .table .table-bordered .table-striped }
+| Name        | Scope    | Description                         | Example          | Type     |
+| ----------- | -------- | ----------------------------------- | ---------------- | -------- |
+| `partnerId` | required | The partner id assigned by concert. | `'partner_name'` | `string` |