[1.10.x] Doc'd how ModelAdmin.list_display uses short_description.

Backport of 8ab8a8910c from master

docs/ref/contrib/admin/index.txt

@@ -634,6 +634,10 @@ subclass::
           :func:`~django.utils.html.format_html_join`, or
           :func:`~django.utils.safestring.mark_safe` instead.
 
+    * As some examples have already demonstrated, when using a callable, a
+      model method, or a ``ModelAdmin`` method, you can customize the column's
+      title by adding a ``short_description`` attribute to the callable.
+
     * If the value of a field is ``None``, an empty string, or an iterable
       without elements, Django will display ``-`` (a dash). You can override
       this with :attr:`AdminSite.empty_value_display`::