update GAE notice

acc. to bcosca/fatfree#884 (comment)

3.6/quick-reference/main.md

@@ -408,7 +408,7 @@ The default serializer used by the [Base->serialize()](base#serialize "Definitio
 
 Temporary folder for cache, filesystem locks, compiled F3 templates, etc. The default value is the `'tmp/'` folder inside the Web root. _Adjust accordingly to conform to your site's security policies_.
 
-When you're using Google App Engine (GAE) to deploy your application, it's recommended to set it to the in-memory file-system with `$f3->set('TEMP', sys_get_temp_dir())`.
+When you're using Google App Engine (GAE) to deploy your application, it's recommended to set it to a cloud storage dir.
 
 
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