title: FieldError: Unknown field(s) (received_time) specified for Event. Check fields/fieldsets/exclude attributes of class EventAdmin
body: <p>I have the following model </p>
  
  <pre><code>class Event(models.Model):
      product_type = models.CharField(max_length=250, null=False, blank=False)
      received_time = models.DateTimeField(editable=False)
  </code></pre>
  
  <p>in admin:</p>
  
  <pre><code>class EventAdmin(admin.ModelAdmin):
      fields = ['product_type', 'received_time']
  </code></pre>
  
  <p>I get the following error when trying to edit an event (clicking on an individual event in the admin):</p>
  
  <pre><code>FieldError at /admin/events/event/20/
  Unknown field(s) (received_time) specified for Event. Check fields/fieldsets/exclude attributes of class EventAdmin.
  </code></pre>
  
  <p>I do see that <code>editable=False</code> but I still want it to at least be <em>visible</em>, even it it isn't editable. Is there a way to fix this error and edit these items in admin? </p>