title: Show a field name instead of the whole object for ManyToMany object in django admin site
body: <p>My models are as follows:</p>
  
  <pre><code>class Retailer(BaseModel):
      brand = models.ManyToManyField('brands.Brand',blank=True)
  
  class Brand(BaseModel):
      name = models.CharField(max_length=100, unique=True)
      website = models.URLField(max_length=500, blank=True, default='')
  </code></pre>
  
  <p>And my admin class is as follows:</p>
  
  <pre><code>class RetailerAdmin(admin.ModelAdmin):
      filter_horizontal = ('brand',)
  </code></pre>
  
  <p>The admin site does show the multi-select field for me, but every entry in the brand list is just shown as <code>Brand object</code>, which makes no sense to me. I want every entry to be shown as the name field of that brand. What should I do?</p>