Merge pull request #8572 from electron/content-tracing-app-ready

Document using content tracing after app ready

docs/api/content-tracing.md

@@ -9,9 +9,14 @@ This module does not include a web interface so you need to open
 `chrome://tracing/` in a Chrome browser and load the generated file to view the
 result.
 
-```javascript
-const {contentTracing} = require('electron')
+**Note:** You should not use this module until the `ready` event of the app
+module is emitted.
 
+
+```javascript
+const {app, contentTracing} = require('electron')
+
+app.on('ready', () => {
   const options = {
     categoryFilter: '*',
     traceOptions: 'record-until-full,enable-sampling'
@@ -26,6 +31,7 @@ contentTracing.startRecording(options, () => {
       })
     }, 5000)
   })
+})
 ```
 
 ## Methods