gistfile1.php

    /**
     * Create and Edit
     * @param \Sonata\AdminBundle\Form\FormMapper $formMapper
     *
     * @return void
     */
    protected function configureFormFields(FormMapper $formMapper)
    {
        $formMapper
            ->with(
               'My Entity Name', 
                array(
                    'description' => "Text added here is displayed onscreen above the form defined below. 
                    <br /> You can even include html tags and they will render as expected, like this 
                    break tag for example! I find this quite useful."
                )
            )
            ->add(
                'dateStart',
                'date',
                array(
                    'widget' => 'single_text',
                    'format' => 'dd/MM/yyyy',
                    'empty_value' => ''
                )
            )
            //more fields here
            ->end();
    }