Symfony2 form help text

config.yml

twig:
    form:
        resources:
            - "Form/form_theme.html.twig"

form.html.twig

{{ form_row(form.title, {help: 'For reference only.'}) }}

form_theme.html.twig

{% extends 'form_div_layout.html.twig' %}

{% block form_row -%}
  <div class="form-group {{ container_class|default(false) }}">
    {{ form_label(form) }}
    {{ form_errors(form) }}
    {{ form_widget(form) }}
    {% if help|default(false) %}
      <div class="help-block">{{ help }}</div>
    {% endif %}
  </div>
{%- endblock form_row %}