title: Django admin manytomany
body: <p>Good day,I try in admin customize forms model with many to many fields</p>
  
  <pre><code>class CasinoForm(forms.ModelForm):
  class Meta():
      model = Casino
  
  country = forms.MultipleChoiceField(choices=CasinoCountries.objects.all().values_list('id', 'name_ru').order_by('name_ru'))
  </code></pre>
  
  <p>When i try save it, it saved but not returned selected, how return selected items</p>