title: Auto-populating user manytomanyfield with Django admin site
body: <p>I have a class Business, example:</p>
  
  <pre><code>class Business(models.Model):
      users = models.ManyToManyField(User)
      business_name = models.CharField(max_length=100)
  </code></pre>
  
  <p>So the variable <code>users</code> in connected with the <code>Use</code>r. And let's assume that in the <code>User</code>, there are 5 users were created: <code>Admin</code>, <code>Test</code>, <code>Test1</code>, <code>Test2</code> and <code>Test3</code>. So only <code>Admin</code> is the superuser of all the users and let's say that I am logged in using <code>Test2</code>. So when I clicked save, the manytomanyfield will be automatically saved with <code>Test2</code>, so it is like automatically saved on whoever the <code>request.user</code> is.</p>
  
  <p>And also, is there a way to automatically save all the users in the manytomanyfield? thanks.</p>