[WIP] Add doc for tel type

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes https://github.com/symfony/symfony/pull/11360 
| Applies to    | all (or 2.3+)
| Fixed tickets | https://github.com/symfony/symfony/issues/8026
this should be moved to the top (before the introduction paragraph)