fix bad link (#1157)

Author: davidkonigsberg

fern/products/docs/pages/api-references/customize-api-ref.mdx

@@ -98,7 +98,7 @@ To reference an endpoint, you can use either:
 
 ### Renaming sections
 
-By default, section display names come from [service file names](/api-definition/fern/endpoints#service-definition) (Fern
+By default, section display names come from [service file names](/api-definitions/ferndef/endpoints/overview#service-definition) (Fern
 Definition) or tag names (OpenAPI) in your spec.
 
 To override the display name of a section, use the `section` property in your `docs.yml` and reference the `lowerCamelCase` version of the original service file name (Fern Definition) or tag name (OpenAPI) in `referenced-packages`.