docs: fix example with redis v4

It seems the clients must be connected before creating the adapter.

Related: #436

Author: darrachequesne

README.md

@@ -48,58 +48,58 @@ const io = new Server();
 const pubClient = createClient({ host: 'localhost', port: 6379 });
 const subClient = pubClient.duplicate();
 
-io.adapter(createAdapter(pubClient, subClient));
-
-// redis@3
-io.listen(3000);
-
-// redis@4
 Promise.all([pubClient.connect(), subClient.connect()]).then(() => {
+  io.adapter(createAdapter(pubClient, subClient));
   io.listen(3000);
 });
 ```
 
-### ES6 modules
+With `redis@3`, calling `connect()` on the Redis clients is not needed:
 
 ```js
-import { Server } from 'socket.io';
-import { createClient } from 'redis';
-import { createAdapter } from '@socket.io/redis-adapter';
+const { Server } = require('socket.io');
+const { createClient } = require('redis');
+const { createAdapter } = require('@socket.io/redis-adapter');
 
 const io = new Server();
 const pubClient = createClient({ host: 'localhost', port: 6379 });
 const subClient = pubClient.duplicate();
 
 io.adapter(createAdapter(pubClient, subClient));
 
-// redis@3
 io.listen(3000);
+```
+
+### ES6 modules
+
+```js
+import { Server } from 'socket.io';
+import { createClient } from 'redis';
+import { createAdapter } from '@socket.io/redis-adapter';
+
+const io = new Server();
+const pubClient = createClient({ host: 'localhost', port: 6379 });
+const subClient = pubClient.duplicate();
 
-// redis@4
 Promise.all([pubClient.connect(), subClient.connect()]).then(() => {
+  io.adapter(createAdapter(pubClient, subClient));
   io.listen(3000);
 });
 ```
 
 ### TypeScript
 
 ```ts
-// npm i -D redis @types/redis
 import { Server } from 'socket.io';
+import { createClient } from 'redis';
 import { createAdapter } from '@socket.io/redis-adapter';
-import { RedisClient } from 'redis';
 
 const io = new Server();
 const pubClient = createClient({ host: 'localhost', port: 6379 });
 const subClient = pubClient.duplicate();
 
-io.adapter(createAdapter(pubClient, subClient));
-
-// redis@3
-io.listen(3000);
-
-// redis@4
 Promise.all([pubClient.connect(), subClient.connect()]).then(() => {
+  io.adapter(createAdapter(pubClient, subClient));
   io.listen(3000);
 });
 ```