Fixed #25531 -- Documented that admin_order_field supports lookups.

          colored_first_name.admin_order_field = '-first_name'

      ``admin_order_field`` supports query lookups to sort by values on related

      models. This example includes an "author first name" column in the list

      display and allows sorting it by first name::

          class Blog(models.Model):

              title = models.CharField(max_length=255)

              author = models.ForeignKey(Person, on_delete=models.CASCADE)

          class BlogAdmin(admin.ModelAdmin):

              list_display = ('title', 'author', 'author_first_name')

              def author_first_name(self, obj):

                  return obj.author.first_name

              author_first_name.admin_order_field = 'author__first_name'

    * Elements of ``list_display`` can also be properties. Please note however,

      that due to the way properties work in Python, setting

      ``short_description`` on a property is only possible when using the