Added warning about get_inline_instances() permission checking; refs #23754.

    filtering based on add, change, and delete permissions::

        class MyModelAdmin(admin.ModelAdmin):

            inlines = (MyInline,)

            def get_inline_instances(self, request, obj=None):

                return [inline(self.model, self.admin_site) for inline in self.inlines]

    If you override this method, make sure that the returned inlines are

    instances of the classes defined in :attr:`inlines` or you might encounter

    a "Bad Request" error when adding related objects.

.. method:: ModelAdmin.get_urls()

    The ``get_urls`` method on a ``ModelAdmin`` returns the URLs to be used for