Update OpenX bidder docs with FPD (prebid#3526)

dev-docs/bidders/openx.md

@@ -15,6 +15,7 @@ userIds: admixerId, adtelligentId, amxId, britepoolId, criteo, dapId, deepintent
 prebid_member: true
 fpd_supported: true
 gvl_id: 69
+fpd_supported: true
 ---
 
 ### Registration
@@ -95,6 +96,42 @@ var adUnits = [
 ];
 ```
 
+#### First Party Data
+OpenX supports FPD configured under `ortb2.user`and `ortb2.site.content` as described [here]((/features/firstPartyData.html)).
+Ad unit specific FPD is not supported, and segment taxonomies (`segtax`) are simply passed through. If you have any 
+questions, please reach out to us at [email protected]
+
+Example: 
+```
+pbjs.setConfig({
+   ...
+   ortb2: {
+       site: {
+            content: {
+                data: [{
+                    name: "www.dataprovider1.com",
+                    ext: { segtax: 4 },
+                    segment: [
+                        { id: "687" },
+                        { id: "123" }
+                    ]
+                }]
+            },
+       },
+       user: {
+           data: [{
+               name: "dataprovider.com",
+               ext: { segtax: 4 },
+               segment: [
+                    { id: "1" }
+               ]
+           }],
+       }
+   }
+   ...
+});
+```
+
 ### Configuration
 Add the following code to enable user syncing. By default, Prebid.js version 0.34.0+ turns off user syncing through iframes.
 OpenX strongly recommends enabling user syncing through iframes. This functionality improves DSP user match rates and increases the