docs: Update link to 'Built-in users' page

README.md

@@ -394,7 +394,7 @@ instead of `elasticsearch`.
 [win-shareddrives]: https://docs.docker.com/docker-for-windows/#shared-drives
 [mac-mounts]: https://docs.docker.com/docker-for-mac/osxfs/
 
-[builtin-users]: https://www.elastic.co/guide/en/x-pack/current/setting-up-authentication.html#built-in-users
+[builtin-users]: https://www.elastic.co/guide/en/elasticsearch/reference/current/built-in-users.html
 [ls-security]: https://www.elastic.co/guide/en/logstash/current/ls-security.html
 [sec-tutorial]: https://www.elastic.co/guide/en/elasticsearch/reference/current/security-getting-started.html