Presumably you already know that DokuWiki installations automatically output a message when you are logged in as superuser and when a new update is available.
In addition, you can subscribe to the "change" page. Then you will receive an e-mail for changes to this page.
https://www.dokuwiki.org/changes?do=subscribe
And as far as I know, you can read this page via RSS too.
HTH - Michael Sy.