[Components][Form] add versionadded for the data collector form extension

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.4+
| Fixed tickets | 

As @ahsio pointed out in #3886, the data collector extension was added to the Form component in Symfony 2.4.
Is there really anything special for you to do? I mean, using the default Sphinx template causes no problems. So, what I was wondering about was if there is something for you to do in the template. Or if this just rendered smoothly.