feature #5008 Added a note about how to enable http_method_override f…

…or caching kernels (javiereguiluz)

This PR was squashed before being merged into the 2.3 branch (closes #5008).

Discussion
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Added a note about how to enable http_method_override for caching kernels

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | 2.3+
| Fixed tickets | #3569

Commits
-------

e719510 Added a note about how to enable http_method_override for caching kernels

book/http_cache.rst

@@ -166,6 +166,24 @@ kernel::
 The caching kernel will immediately act as a reverse proxy - caching responses
 from your application and returning them to the client.
 
+.. caution::
+
+    By default, a kernel based on the cache ignores the ``framework.http_method_override``
+    option, which could lead to errors when using ``PUT``, ``DELETE`` and ``PURGE``
+    methods in HTTP requests.
+
+    Invoke the ``enableHttpMethodParameterOverride()`` method before creating the
+    ``Request`` object in order to take this option into account::
+
+        // web/app.php
+
+        // ...
+        $kernel = new AppCache($kernel);
+
+        Request::enableHttpMethodParameterOverride(); // <-- add this line
+        $request = Request::createFromGlobals();
+        // ...
+
 .. tip::
 
     The cache kernel has a special ``getLog()`` method that returns a string