Wrong documentation for Form::addFieldsFromDca()

[tristanlins]

https://github.com/codefog/contao-haste/blob/release/4.1.0/docs/Form/Form.md#add-the-form-fields-from-a-back-end-dca

The callback is called for each single field, with field name and field config as values, the documentation says that the callback is called one time with an array of fields.