update doc

Author: ysmood

custom-launch.md

@@ -108,6 +108,22 @@ Here are the available flags: [link](https://peter.sh/experiments/chromium-comma
 
 Read the API doc for more info: [link](https://pkg.go.dev/github.com/go-rod/rod/lib/launcher#Launcher).
 
+## Cleanup
+
+By default, the browser will create a [user-data-dir](https://chromium.googlesource.com/chromium/src/+/master/docs/user_data_dir.md)
+to store the user data, such as cookies, cache, etc.
+Rod provides a helper function `Cleanup` to remove it after the browser is fully closed:
+
+```go
+func main() {
+	l := launcher.New().
+		Headless(false).
+		Devtools(true)
+
+	defer l.Cleanup()
+}
+```
+
 ## Remotely manage the launcher :id=remotely-manage-the-launcher
 
 For production scraping system, usually, we will separate the scrapers and browsers into different clusters so that
@@ -124,7 +140,8 @@ Here's an example to use it:
 2. Open another terminal and run code like this [example](https://github.com/go-rod/rod/blob/main/lib/examples/launch-managed/main.go)
 
 The image is [tuned](https://github.com/go-rod/rod/blob/main/lib/docker/Dockerfile) for screenshots and fonts among popular natural languages.
-Each container can launch multiple browsers at the same time.
+Each container can launch multiple browsers at the same time. The manager will automatically remove the [user-data-dir](https://chromium.googlesource.com/chromium/src/+/master/docs/user_data_dir.md)
+when the control connection is closed.
 
 ## User mode :id=user-mode