Notes about caching pages with a CSRF Form

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | no
| Applies to    | all
| Fixed tickets | #1216
@weaverryan  I am looking at the Symfony2 HTTPCache and docs and saw this:

- In the docs, it is not 100% explicit but it mentions that in presence of cookies, caches don´t do anything, check http://symfony.com/doc/current/book/http_cache.html#caching-rules-and-defaults

- Looking at the code, you can see this behaviour at https://github.com/symfony/symfony/blob/master/src/Symfony/Component/HttpKernel/HttpCache/HttpCache.php#L675:L690

As the docs say, Varnish, Squid, the HTTPCache component or basically any HTTP cache system does not do anything for non-safe methods or the presence of things like cookies unless you manually enable it. And if you enable it, you should know what you are doing (even if it is a terrible idea anyway :))

Thoughts?