Added a note against using the Apache Router

Author: javiereguiluz

cookbook/configuration/apache_router.rst

@@ -4,6 +4,15 @@
 How to Use the Apache Router
 ============================
 
+.. caution::
+
+    **Using the Apache Router is no longer considered a good practice**.
+    The small increase obtained in the application routing performance is not
+    worth the hassle of continuously updating the routes configuration.
+
+    The Apache Router will be removed in Symfony 3 and it's highly recommended
+    to not use it in your applications.
+
 Symfony, while fast out of the box, also provides various ways to increase that
 speed with a little bit of tweaking. One of these ways is by letting Apache
 handle routes directly, rather than using Symfony for this task.