title: Django CheckBox Form Item using choices not true / false (Boolean)
body: <p>This is driving me bonkers and hopefully someone can point me in the right direction to change this.  I've got a Boolean item in my Model, however when I create my form it gives a Choice option with "Unknown", "Yes" and "No".  I thought it would default to "True" and "False" so need to change this accordingly.  My initial thought was to use a Widget (like I've done to set Textarea's up, but cannot seem to find a model or widget .boolean option.  If anyone can steer me right I'd really appreciate it :)</p>
  
  <p>Code below incase its of use, I'm only 2 months into learning Django / Python (in my spare time which isn't a lot with a 4 month old) so the code may not be as good as someone with a lot of experience.</p>
  
  <p>Thanks in advance :)</p>
  
  <p>Model</p>
  
  <pre><code>class Announcement(models.Model):
      announcement_title = models.CharField(max_length=75, verbose_name="Announcement Title")
      announcement_text = models.CharField(max_length=500, verbose_name="Announcement Text")
      announcement_active = models.BooleanField(default=True, verbose_name="Announcement Active")
      announcement_date = models.DateField(default=date.today, verbose_name="Announcement Date")
      announcement_high = models.BooleanField(default=True, verbose_name="Announcement Alert Severity")
      announcement_expiry = models.DateField(null=True, verbose_name="Announcement Expiry")
  
      def __str__(self):
          return self.announcement_text
  </code></pre>
  
  <p>Form</p>
  
  <pre><code>class AnnouncementForm(ModelForm):
      class Meta:
          model = Announcement
          exclude = ('announcement_date', 'announcement_active', )
          help_texts = {
              'announcement_title': _('Enter a title to give the announcement.'),
              'announcement_text': _('Type the announcement body in this box.'),
              'announcement_expiry': _('Can specify a date to stop displaying the announcement. Can be left blank.'),
              'announcement_high': _('Tick this box to indicate a red severity, un-ticked will make it yellow.'),
          }
          widgets = {
              'announcement_title': forms.TextInput(attrs={'class': 'form-control'}),
              'announcement_text': forms.Textarea(attrs={'class': 'form-control', 'cols': 80, 'rows': 10}),
              'announcement_expiry': widgets.DateInput(attrs={'class' : 'datepicker'}),
          }
  </code></pre>
  
  <p>View</p>
  
  <p>Quite big so not sure if this is needed. Can post if required.</p>
  
  <p>Template</p>
  
  <pre><code>&lt;form action="/siteadmin/{{ branding.dataset }}" method="POST" class="form-horizontal"&gt;
      {% csrf_token %}
      {% for item in form %}
      &lt;div class="form-group"&gt;
          &lt;div class="col-sm-4 control-label"&gt;
          {% if item.help_text %}
              &lt;img src="/static/images/info.png" height="20" width="20" aria-hidden="true" data-toggle="popover" title="{{ item.help_text }}"&gt;&amp;nbsp
          {% endif %}
              {{ item.label_tag }}
          &lt;/div&gt;
          &lt;div class="col-sm-7"&gt;
              {{ item }}
          &lt;/div&gt;
          &lt;div class="col-sm-1"&gt;
          &lt;/div&gt;
      &lt;/div&gt;
      {% endfor %}
      &lt;div class="form-group"&gt;    
          &lt;div class="col-sm-11"&gt;
              &lt;input class="btn btn-primary pull-right" type="submit" value="Add" /&gt;
          &lt;/div&gt;
          &lt;div class="col-sm-1"&gt;
          &lt;/div&gt;
      &lt;/div&gt;  
  &lt;/form&gt;
  </code></pre>