Update debugger.md

I wasted >1h trying to find out why the debug bar was not shown on my remote staging server. Hopefully this will help other people avoid this mistake...

docs/guide/debugger.md

@@ -10,6 +10,17 @@ Installing and configuring
 How to use it
 -------------
 
+Add these lines to your config file:
+
+```
+    'preload' => ['debug'],
+    'modules' => [
+            'debug' => ['yii\debug\Module']
+        ]
+```
+
+**Watch out: by default the debug module only works when browsing the website from the localhost. If you want to use it on a remote (staging) server, add the parameter allowedIPs to the config to whitelist your IP.**
+
 Creating your own panels
 ------------------------