I wondered why I always put form definitions in `AppBundle/Form/Type`, and whether we were meant to put something else in `AppBundle/Form`. While Googling for an answer I came acrosshttp://symfony.com/doc/current/best_practices/forms.html which says the new best practice is to put the form types (which I guess are usually form definitions) directly in `AppBundle/Form`.This PR updates the [main documentation ](http://symfony.com/doc/current/book/forms.html#book-form-creating-form-classes) to reflect the best practices. If anyone can point me to discussions clarifying the difference between form types, form definitions and how the Symfony view has changed (reflected in the change of location) I'd greatly appreciate it.