my_form.html

{% load add_class %}
<form method="post">
    {% csrf_token %}
    {{ form.non_field_errors }}
    {% for field in form %}
    <div class="form-group">
      {{field.label_tag}}
      {{field | add_class:"form-control"}}
      {{field.errors}}
    </div>

    {% endfor %}

    <div class="form-group">
      <button type="submit" class="btn btn-primary">Cadastrar</button>
    </div>
</form>