Update devtools-extension with a note about it not working

docs/tutorial/devtools-extension.md

@@ -8,6 +8,8 @@ the `BrowserWindow.addDevToolsExtension` API to load them. The loaded extensions
 will be remembered so you don't need to call the API every time when creating
 a window.
 
+** NOTE: React DevTools does not work, follow the issue here https://github.com/atom/electron/issues/915 **
+
 For example, to use the [React DevTools Extension](https://github.com/facebook/react-devtools)
 , first you need to download its source code: