vi bid adapter docs (#537)

* vi bid adapter docs

* VI bid adapter docs - added header

* VI adapter docs - renamed file and changed according to example

dev-docs/bidders/vi.md

@@ -0,0 +1,21 @@
+---
+layout: bidder
+title: vi
+description: vi bid adapter
+top_nav_section: dev_docs
+nav_section: reference
+hide: true
+biddercode: vi
+biddercode_longer_than_12: false
+prebid_1_0_supported : true
+---
+
+### bid params
+{: .table .table-bordered .table-striped }
+| Name          | Scope    | Description                                     | Example                           |
+| :------------ | :------- | :---------------------------------------------- | :--------------------------------- |
+| `pubId` | required | Publisher ID, provided by vi           | 'sb_test' |
+| `lang`      | required | Ad language, in ISO 639-1 language code format  | 'en-US', 'es-ES', 'de'              |
+| `cat`      | required | Ad IAB category (top-level or subcategory), single one supported  | 'IAB1', 'IAB9-1'        |
+| `bidFloor`      | optional | Lowest value of expected bid price  | 0.001        |
+