title: Django UpdateView disable some fields
body: <p>I have made a class view inheriting UpdateView. I have specified the fields and models from which the forms should be built. Now say if i have a field email, then I want to disable it in the form. I have no clues as to how it can be done.</p>
  
  <pre><code>class UserUpdate(UpdateView):
      model = Users
      fields = ['email', 'first_name', 'last_name', 'birth_date']
      template_name = 'users_update_form.html'
      success_url = '/index/'
  </code></pre>