Fix socketio sample

The sample provided was not working as it tried to use `polling`, which is unsupported by the notification URL you get back.

I included the socket IO library and added a websocket as the transport protocol to make it work.

Author: estruyf

api-reference/v1.0/api/subscriptions-socketio.md

@@ -113,17 +113,30 @@ The `notificationUrl` returned is a socket.io endpoint URL.
 
 The following example shows how to use the `notificationUrl` with socket.io in JavaScript.
 
-```javascript
-// this is the notificationUrl returned from this API
-var notificationUrl = "https://f3hb0mpua.svc.ms/zbaehwg/callback?snthgk=1ff3-2345672zz831837523";
-
-// 'io' comes from the socket.io client library
-var socket = io(notificationUrl);
-
-// these examples log to the console.
-// your app would provide its own callbacks
-socket.on("connect", ()=>console.log("Connected!"));
-socket.on("notification", (data)=>console.log("Notification!", data));
+```html
+<script src="https://cdnjs.cloudflare.com/ajax/libs/socket.io/4.8.1/socket.io.js"></script>
+<script>
+  // This is the notificationUrl returned from this API
+  var notificationUrl = "https://f3hb0mpua.svc.ms/zbaehwg/callback?snthgk=1ff3-2345672zz831837523";
+  
+  // 'io' comes from the socket.io client library
+  var socket = io(notificationUrl, {
+    transports: ['websocket'] // Make sure to use "websocket" as the default is set to "polling" which is not supported
+  });
+  
+  socket.on("connect", () => {
+    console.log(`connect`, socket.id);
+  });
+  
+  socket.on("disconnect", () => {
+    // Returns "undefined" on disconnect
+    console.log(`disconnect`, socket.id);
+  });
+  
+  socket.on("notification", (data) => {
+    console.log(`Notification received:`, data);
+  });
+</script>
 ```
 
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