PhonelistPage: add search_description to index

The PhonelistPage doesn't inherit from BodyMixin.

Define our search_fields explicitly.

mpicms/base/models.py

@@ -10,6 +10,7 @@
 from wagtail.admin.edit_handlers import StreamFieldPanel
 from wagtail.images.edit_handlers import ImageChooserPanel
 from wagtail.core.fields import StreamField
+from wagtail.search import index
 
 from mpicms.news.mixins import NewsMixin
 from mpicms.events.mixins import EventMixin
@@ -121,6 +122,9 @@ class Meta: # noqa
 class PhonelistPage(BasePage):
     content_panels = Page.content_panels
     promote_panels = Page.promote_panels
+    search_fields = [
+        index.SearchField("search_description"),
+    ]
 
     class Meta: # noqa
         verbose_name = _("Phonelist")