To do that you do not need to use any bundle. You can implement a jquery text editor, such as redactor, ckeditor..
In your FormType just pass a class variable which appropriate with your wsyiwyg editor. For example you use Redactor to make it possible.
<script type="text/javascript">
$(document).ready(function(){
$('.redactor').redactor();
});
</script>
In your FormType you must build a textarea with a class "redactor". To do that:
$builder->add('content', 'textarea', array('label' => "Content", 'attr' => array("class" => "redactor", "style" => "height: 300px")));
Finally, in your Twig print the content row:
{{ form_row(form.content) }}