title: Query for top x elements in Django
body: <p>I have two models such that</p>
  
  <pre><code>class JobTitle(models.Model):
       name = models.CharField(max_length=1000)
  
  class Employer(models.Model): 
       jobtitle = models.ForeignKey(JobTitle,unique=False,null=True)
  </code></pre>
  
  <p>As you see, one employer may have many jobtitles. I try to make a query to get top 5 employers whose number of job titles is maximum</p>
  
  <p>How can I achive this is Django ?</p>
  
  <p>Thanks</p>