feature #3446 [WCM] Documented deprecation of the apache router. (jakzal)

This PR was merged into the master branch.

Discussion
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[WCM] Documented deprecation of the apache router.

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | no
| Applies to    | 2.5+
| Fixed tickets | -

Commits
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fdf4891 Documented deprecation of the apache router.

Author: weaverryan

cookbook/configuration/apache_router.rst

@@ -7,6 +7,12 @@ How to use the Apache Router
 Symfony2, 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 Symfony2 for this task.
 
+.. note::
+
+    Apache router was deprecated in Symfony 2.5 and will be removed in Symfony 3.0.
+    Since the PHP implementation of the Router was improved, performance gains were no longer
+    significant (while it's very hard to replicate the same behaviour).
+
 Change Router Configuration Parameters
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