frontend user-identity method (#232)

* Update user-identity.mdx

* Update user-identity.mdx

Add beta message with limitations

Author: shalomgk

fern/docs/pages/sdks/web/user-identity.mdx

@@ -120,3 +120,46 @@ const sessionToken = '<SESSION_TOKEN>'
         })})();
 </script>
 ```
+
+## Identify users without session token
+
+You can also pass the identifiers in the `plugSDK.init` option without generating the session token.
+
+<Callout intent="note">
+This frontend user identification, by its nature, is not secure as the data is transmitted through the client side. It is recommended to use the session token method to securely identify users.
+</Callout>
+
+<Callout intent="warning">
+This method is currently in beta and comes with the following limitations:
+- Unverified users cannot be converted or merged into verified users.
+- An external reference used by an unverified user cannot be reused for any other user.
+</Callout>
+
+```jsx
+window.plugSDK.init({
+  app_id: '<your_unique_app_id>',
+  identity: {
+    user_ref: string;
+    user_traits?: { // optional
+      custom_fields?: object; // optional
+      display_name?: string; // optional
+      email?: string; // optional
+      phone_numbers?: string[]; // optional
+    }
+  }
+})
+```
+
+You can add or update the data in `user_traits` by using the `updateIdentity` method on the PLuG SDK. Attached is a sample code snippet for the same. 
+
+```jsx
+window.plugSDK.updateIdentity({
+  user_traits: {
+    custom_fields?: object; // optional
+    display_name?: string; // optional
+    email?: string; // optional
+    phone_numbers?: string[]; // optional
+  }
+})
+```
+