title: Following Manual Instructions for Bootstrap 3 forms getting yml config error
body: <p>I'm following directions directly from the manual. I've got this configuration setting in my config.yml</p>
  
  <pre><code>twig:
      form:
          resources: ['bootstrap_3_layout.html.twig']
  </code></pre>
  
  <p>haven't got this far but in my base.html.twig i have...</p>
  
  <pre><code>    &lt;link rel="stylesheet" 
            href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css" 
            integrity="sha384-1q8mTJOASx8j1Au+a5WDVnPi2lkFfwwEAa8hDDdjZlpLegxhjVME1fgjWPGmkzs7" 
            crossorigin="anonymous"&gt;
  
      &lt;!-- Optional theme --&gt;
      &lt;link rel="stylesheet" 
            href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap-theme.min.css" 
            integrity="sha384-fLW2N01lMqjakBkx3l/M9EahuwpSfeNvV63J5ezn3uZzapT0u7EYsXMjQV+0En5r" 
            crossorigin="anonymous"&gt;
      {% block stylesheets %}{% endblock %}
  </code></pre>
  
  <p>And of course the appropriate call for jquery and boostrap.js at bottom of base.html.twig</p>
  
  <p>In any of my templates I have....</p>
  
  <pre><code>{% extends 'base.html.twig' %}
  {% form_theme form 'bootstrap_3_layout.html.twig' %}
  
  
  {% block body %} //etc. etc.
  </code></pre>
  
  <p>I get the error:</p>
  
  <pre><code>InvalidConfigurationException in ArrayNode.php line 317:
  Unrecognized option "form" under "twig"
  </code></pre>
  
  <p>did they change the yml configuration settings and not update it in the manual?</p>