guide: fix broken link

Author: flatcap

guide/optionalfeatures.html

@@ -432,7 +432,7 @@ <h2 class="title" style="clear: both">
     <code class="literal">mutt_oauth2.py</code> script written by Alexander Perlis:
     <a class="ulink" href="https://github.com/neomutt/neomutt/blob/main/contrib/oauth2/mutt_oauth2.py" target="_top">https://github.com/neomutt/neomutt/blob/main/contrib/oauth2/mutt_oauth2.py</a></p>
     <p>You'll need to get your own oauth client credentials by following the script instructions:
-    <a class="ulink" href="https://github.com/neomutt/neomutt/blob/main/contrib/oauth2/mutt_oauth2.py.README" target="_top">https://github.com/neomutt/neomutt/blob/main/contrib/oauth2/mutt_oauth2.py.README</a></p>
+    <a class="ulink" href="https://github.com/neomutt/neomutt/blob/main/contrib/oauth2/README.md" target="_top">https://github.com/neomutt/neomutt/blob/main/contrib/oauth2/README.md</a></p>
     <pre class="screen">
 set imap_authenticators="xoauth2"
 set imap_oauth_refresh_command="/path/to/mutt_oauth2.py /path/to/token"