webapp/templates/default/module/room.html.twig

  <form name="room" action="{{ path('room_add') }}" method="post">
      {% if error %}
          <output name="error" for="form-room-name">{{ error }}</output>
      {% endif %}
      <input type="text" name="name" id="form-room-name" value="{{ name }}" placeholder="{{ 'enter new room name...' | trans }}" />
      <button type="submit">{{ 'add' | trans }}</button>
  </form>