title: use Crispy form with ModelForm
body: <p>I've been running into <a href="http://django-crispy-forms.readthedocs.org/en/latest/index.html" rel="noreferrer">crispy form</a>, and it seems to do exactly what I want: render forms with bootstrap layout.</p>
  
  <p>Now, the example talk about using <code>forms.Form</code>. This is ok, I can create mine by writing the code like this:</p>
  
  <pre><code>class TemplateCreateForm(forms.Form):
      title = forms.CharField(label=(u'Task name'))
      description = forms.CharField(label=(u'Task description'))
      url_start = forms.CharField(label=(u'Start page url'))
      url_end = forms.CharField(label=(u'Final page url'))
  
      def __init__(self, *args, **kwargs):
          self.helper = FormHelper()
          self.helper.form_method = 'post'
          self.helper.add_input(Submit('submit', 'Submit'))
          super(TemplateCreateForm, self).__init__(*args, **kwargs)
  </code></pre>
  
  <p>But, how to do the update? because if I put this in the view:</p>
  
  <pre><code>    form = TemplateCreateForm(request.POST or None, instance=template)
  </code></pre>
  
  <p>it does not work because <strong>instance is only for ModelForm.</strong></p>
  
  <p>Now, can I substitute the <code>forms.Form</code> with <code>ModelForm</code> and use crispy form for ModelForm?
  I did this</p>
  
  <pre><code>class TemplateCreateForm(ModelForm):
      title = forms.CharField(label=(u'Task name'))
      description = forms.CharField(label=(u'Task description'))
      url_start = forms.CharField(label=(u'Start page url'))
      url_end = forms.CharField(label=(u'Final page url'))
  
      def __init__(self, *args, **kwargs):
          self.helper = FormHelper()
          self.helper.form_method = 'post'
          self.helper.add_input(Submit('submit', 'Submit'))
          super(TemplateCreateForm, self).__init__(*args, **kwargs)
  
      class Meta:
          model = Template
          exclude = ('user')
  </code></pre>
  
  <p>Here I added the Meta class.
  Now: it works,  but is it correct to use it like this?
  The update works as well in this way.</p>
  
  <p>What's the correct way to use forms for doing the update?</p>