Move content_panels inside FormPage definition.

docs/reference/contrib/forms.rst

@@ -37,8 +37,7 @@ Within the ``models.py`` of one of your apps, create a model that extends ``wagt
         intro = RichTextField(blank=True)
         thank_you_text = RichTextField(blank=True)
 
-    FormPage.content_panels = [
-        FieldPanel('title', classname="full title"),
+        content_panels = AbstractEmailForm.content_panels + [
             FieldPanel('intro', classname="full"),
             InlinePanel('form_fields', label="Form fields"),
             FieldPanel('thank_you_text', classname="full"),