add note to readme about VSCode extension (sveltejs#175)

README.md

@@ -35,6 +35,7 @@ Navigate to [localhost:5000](http://localhost:5000). You should see your app run
 
 By default, the server will only respond to requests from localhost. To allow connections from other computers, edit the `sirv` commands in package.json to include the option `--host 0.0.0.0`.
 
+If you're using [Visual Studio Code](https://code.visualstudio.com/) we recommend installing the official extension [Svelte for VS Code](https://marketplace.visualstudio.com/items?itemName=svelte.svelte-vscode). If you are using other editors you may need to install a plugin in order to get syntax highlighting and intellisense.
 
 ## Building and running in production mode