Update adding.md

Author: svrnm

content/en/ecosystem/registry/adding.md

@@ -21,6 +21,6 @@ guidelines][].
   https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/creating-a-pull-request
 [registry-entry.yml]:
   https://github.com/open-telemetry/opentelemetry.io/tree/main/templates/registry-entry.yml
-[marketing guidelines]: https://opentelemetry.io/community/marketing-guidelines/
+[marketing guidelines]: /community/marketing-guidelines/
 [trademark usage guidelines]:
   https://www.linuxfoundation.org/legal/trademark-usage