docs: important when using config caching

Author: ddevsr

user_guide_src/source/concepts/factories.rst

@@ -274,7 +274,7 @@ Config Caching
 
 .. important:: Do not use this feature unless you have carefully read this section
     and understand how this feature works. Otherwise, your application will not
-    function properly.
+    function properly. Escpecially when you using function ``config()``, you must extends ``BaseConfig``.
 
 To improve performance, Config Caching has been implemented.