Add doc for 1ad4good.org bidder (#1428)

* adding doc for 1ad4good bidder

* header, notes

removed unnecessary header items and the statement about being similar to appnexus -- I found it confusing because appnexus has many more parameters and would guess their test placement IDs values won't work for you.

dev-docs/bidders/1ad4good.md

@@ -0,0 +1,18 @@
+---
+layout: bidder
+title: 1ad4good
+description: Prebid One Ad for Good(1ad4good.org) Bidder Adaptor
+hide: true
+biddercode: 1ad4good
+---
+
+### Note:
+This adapter is for displaying free ads for various not profits. You can find more info at [1ad4good.org])(http://1ad4good.org).
+
+### Bid Params
+
+{: .table .table-bordered .table-striped }
+| Name          | Scope    | Description | Example | Type     |
+|---------------|----------|-------------|---------|----------|
+| `placementId` | required |  Meaningless, but required id          | `234234`   | `integer` |
+| `cpm`         | optional | forces bidder to insert custom cpm bid            |   0.50      | `decimal`  |