feat: add yandex id system docs

dev-docs/modules/userid-submodules/yandex.md

@@ -0,0 +1,30 @@
+---
+layout: userid
+title: Yandex ID
+description: Yandex User ID sub-module
+useridmodule: yandexIdSystem
+---
+
+Yandex ID module is designed to improve the personalization of ads for publishers' users. This documentation provides information about the Yandex User ID module, and instructions to install it. 
+
+## Step 1. Add Yandex ID to Prebid.js package
+
+Add the module to your Prebid.js package:
+
+{: .alert.alert-info :}
+gulp build --modules=yandexIdSystem
+
+## Step 2. Enable Yandex ID
+
+Include the following call to `setConfig` in your Prebid.js code:
+
+```javascript
+pbjs.setConfig({
+    userSync: {
+        userIds: [{
+            name: 'yandex',
+            bidders: ['yandex'],
+        }]
+    }
+});
+```