Update v3-to-v4.md (#1737)

* Update v3-to-v4.md

* Update v3-to-v4.md

* Update v3-to-v4.md

* Update docs/v3-to-v4.md

Co-authored-by: Simon Prickett <[email protected]>

* Update docs/v3-to-v4.md

Co-authored-by: Simon Prickett <[email protected]>

* Update docs/v3-to-v4.md

Co-authored-by: Simon Prickett <[email protected]>

* Update docs/v3-to-v4.md

Co-authored-by: Simon Prickett <[email protected]>

* Update docs/v3-to-v4.md

Co-authored-by: Simon Prickett <[email protected]>

* Update docs/v3-to-v4.md

Co-authored-by: Simon Prickett <[email protected]>

Co-authored-by: Leibale Eidelman <[email protected]>
Co-authored-by: Simon Prickett <[email protected]>

Author: 3 people

docs/v3-to-v4.md

@@ -2,14 +2,54 @@
 
 Version 4 of Node Redis is a major refactor. While we have tried to maintain backwards compatibility where possible, several interfaces have changed. Read this guide to understand the differences and how to implement version 4 in your application.
 
-## Breaking Changes
+## All of the Breaking Changes
 
 See the [Change Log](../packages/client/CHANGELOG.md).
 
-## Promises
+### Promises
 
 Node Redis now uses native [Promises](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) by default for all functions.
 
+### `createClient`
+
+The configuration object passed to `createClient` has changed significantly with this release. See the [client configuration guide](./client-configuration.md) for details.
+
+### No Auto Connect
+
+In V4, the client does not automatically connect to the server, you need to run `.connect()` before any command, or you will receive error `ClientClosedError: The client is closed`.
+
+```typescript
+import { createClient } from 'redis';
+
+const client = createClient();
+
+await client.connect();
+
+await client.ping();
+```
+
+### No `message` event
+
+In V4, you don't need to add listener to the `message` and `message_buffer` events, you can get the message directly in `subscribe`-like commands.
+
+The second argument of these commands is a callback, which will be triggered every time there is a message published to the channel.
+
+The third argument to these commands is a boolean to set `bufferMode` (default `false`).  If it's set to `true` you will receive a buffer instead of a string.
+
+The `subscribe`-like commands return a promise. If the server returns `ok` the promise will be fulfilled, otherwise the promise will be rejected.
+
+```typescript
+import { createClient } from 'redis';
+
+const subscriber = createClient();
+
+await subscriber.connect();
+
+await subscriber.subscribe('channel_name', (message, channelName) => {
+    console.info(message, channelName);
+});
+```
+
 ## Legacy Mode
 
 Use legacy mode to preserve the backwards compatibility of commands while still getting access to the updated experience:
@@ -29,7 +69,3 @@ await client.v4.set('key', 'value', {
     NX: true
 });
 ```
-
-## `createClient`
-
-The configuration object passed to `createClient` has changed significantly with this release. See the [client configuration guide](./client-configuration.md) for details.