Rename docs page to 'Using forms in admin views'

docs/extending/forms.md

@@ -1,4 +1,4 @@
-# Forms
+# Using forms in admin views
 
 [Django's forms framework](https://docs.djangoproject.com/en/stable/topics/forms/) can be used within Wagtail admin views just like in any other Django app. However, Wagtail also provides various admin-specific form widgets, such as date/time pickers and choosers for pages, documents, images and snippets. By constructing forms using `wagtail.admin.forms.models.WagtailAdminModelForm` as the base class instead of `django.forms.models.ModelForm`, the most appropriate widget will be selected for each model field. For example, given the model and form definition: