Gjirafa bidder params documentation (#483)

* Gjirafa bidder params documentation

* Add Prebid 1.0 supported line

* Change prebid support line

dev-docs/bidders/gjirafa.md

@@ -0,0 +1,30 @@
+
+---
+prebid_1_0_supported : true
+layout: bidder
+title: Gjirafa
+description: Prebid Gjirafa Bidder Adaptor
+
+top_nav_section: dev_docs
+nav_section: reference
+
+hide: true
+
+biddercode: gjirafa
+
+biddercode_longer_than_12: false
+
+
+---
+
+### Note:
+The Gjirafa Header Bidding adapter requires to have: placementId param in place OR minCPM and minCPC params.
+
+### bid params
+
+{: .table .table-bordered .table-striped }
+| Name | Scope | Description | Example |
+| :--- | :---- | :---------- | :------ |
+| `placementId` | optional | Your PlacementId (provided by Gjirafa) | `71-1` |
+| `minCPM` | optional | The minCPM for units returned by Gjirafa (required if placementId is not provided) | `0.50` |
+| `minCPC` | optional | The minCPC for units returned by Gjirafa (required if placementId is not provided) | `0.50` |