pbjs.renderAd Doc: Updated to include details about the ${CLICKTHROUG…

…H} macro feature (prebid#4176)

* updated docs for ${CLICKTHROUGH} macro with renderAd func

* spacing update to md file

dev-docs/publisher-api-reference/renderAd.md

@@ -1,6 +1,6 @@
 ---
 layout: api_prebidjs
-title: pbjs.renderAd(doc, id)
+title: pbjs.renderAd(doc, id, options)
 description:
 ---
 
@@ -9,9 +9,22 @@ This function will render the ad (based on params) in the given iframe document
 
 **Kind**: static method of pbjs API
 
+`options.clickThrough` optionally enables publishers to count clicks on prebid inventory in their distributing adserver.
+The publisher may call renderAd with a third param accepting an object where the value of clickThrough will be checked.
+If this property is set the value of clickThrough will replace any occurrence of ${CLICKTHROUGH} inside of the properties ad and adUrl. If no match is found nothing will be replaced.
+
+{: .alert.alert-info :}
+Note: In regards to `options.clickThrough`:
+- To make use of this feature, bid adapters would be required to respond with ad tags including the ${CLICKTHROUGH} macro.
+- The renderAd function must be invoked with the options argument. Ex: `renderAd(doc, bidId, {clickThrough: 'https://someadserverclickurl.com'});`
+- Not compatible with safeframes (since the logic around rendering safeframe's does not invoke the renderAd function).
+- Not supported with Prebid Universal Creative at this time, only the standard pbjs.renderAd method.
+
 
 {: .table .table-bordered .table-striped }
 | Param | Scope | Type | Description |
 | --- | --- | --- | --- |
 | doc | Required | `object` | document |
 | id | Required | `string` | bid id to locate the ad |
+| options | Optional | `object` | object containing other additional params to be used (listed below) |
+| options.clickThrough | Optional | `string` | a url used to keep track of clicks on the ad to be rendered (used to resolve the ${CLICKTHROUGH} macro) |