Update big number documentation

- big number uses the component wrapper helper, but was missing this line in the documentation that shows information about the wrapper in the component guide page for this component

app/views/govuk_publishing_components/components/docs/big_number.yml

@@ -9,6 +9,7 @@ accessibility_criteria: |
   - convey the meaning of the number shown
 shared_accessibility_criteria:
 - link
+uses_component_wrapper_helper: true
 examples:
   default:
     data: