docs: Added the nuxt.config.js setting for ngrok.auth (#10)

Author: tebb

docs/content/en/options.md

@@ -40,6 +40,14 @@ If you don't want your Dev server to be exposed to the internet then you should
 NGROK_AUTH='user:pwd'
 ```
 
+```js{}[nuxt.config.js]
+export default {
+ ngrok: {
+    // module options
+    auth: process.env.NGROK_AUTH
+  }
+}
+```
 <alert type="warning">
 
 Don't forget to make sure your `.env`file has been added to your `.gitignore`.