add example

install/usr/share/swarmlab.io/sec/project/courses/example-helloworld/app/server.js

@@ -4,17 +4,17 @@ var http = require('http').Server(app);
 var io = require('socket.io')(http);
 
 
+app.get('/', (req, res) => {
+  res.send('<h1>Hello world!</h1>');
+});
+
 
 io.on('connection', s => {
       console.error('socket connection');
 
    s.on('log', (data, room) => {
-      s.to('iot').emit('message', data);
       console.log('broadcast', data);
-
   });
-    //s.emit('message', 'message from server');
-
 
 
 });