Updated readme for web (#754)

web/readme.md

@@ -10,27 +10,16 @@ https://flutter.github.io/samples/#?platform=web.
 
 ## Building samples code
 
-Update Flutter and enable web support
-
-```console
-$ flutter channel dev
-$ flutter upgrade
-$ flutter config --enable-web
-```
-
 Run the demo using the `chrome` device type:
 
 ```console
-$ cd slide_puzzle
+$ cd charts
 $ flutter packages get
 $ flutter run -d chrome
 ```
 
 You should see a message printing the URL to access: `http://localhost:8080`
 
-Web support is available as a technical preview and is only available in the
-`dev` or `master` channels.
-
 ## Deploying to GitHub Pages
 
 This project uses [peanut][peanut] to build the samples and commit the output