add Pub-X dev-docs (prebid#2287)

Author: Pub-X

dev-docs/bidders/pubx.md

@@ -0,0 +1,20 @@
+---
+layout: bidder
+title: Pub-X 
+description: Prebid Pub-X Bidder Adapter
+biddercode: pubx
+media_types: banner
+gdpr_supported: false
+coppa_supported: false
+usp_supported: false
+schain_supported: true
+pbjs: true
+---
+
+
+### Bid Params
+
+{: .table .table-bordered .table-striped }
+| Name | Scope    | Description | Example  | Type     |
+|-------|----------|---------------------------|----------|----------|
+| `sid` | required | The AdUnit ID from Pub-X | `'eDMR'` | `string` |