Include missing import of FieldPanel

docs/reference/pages/model_recipes.rst

@@ -268,6 +268,7 @@ To add the tag interface, add the following block of code to a ``wagtail_hooks.p
 .. code-block:: python
 
     from wagtail.contrib.modeladmin.options import ModelAdmin, modeladmin_register
+    from wagtail.admin.edit_handlers import FieldPanel
     from taggit.models import Tag