Notes about caching pages with a CSRF Form

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | no
| Applies to    | all
| Fixed tickets | #1216
I know, but since this is the Default CSRF implementation I thought it was a good idea to use it as an example. Perhaps it can be rephrased and show the Symfony implementation as an example for people who is new to all this type of protection