add redirect for broken link

Author: devalog

fern/docs.yml

@@ -431,6 +431,9 @@ redirects:
   - source: /learn/user-feedback
     destination: /learn/docs/user-feedback
     permanent: true
+  - source: /learn/docs/customization/what-is-docs-yml
+    destination: /learn/docs/configuration/what-is-docs-yml
+    permanent: true
 
   # ============================================================================
   # CLI & API REFERENCE REDIRECTS