Updated Authentication methods (markdown)

Authentication-methods.md

@@ -40,6 +40,8 @@ use_openid: true
 openid_provider_url: https://accounts.google.com
 openid_client_id: your-client-id
 openid_client_secret: your-client-secret
+# openid_email_whitelist:
+  - marco.piovanello@gmail.com
 
 # localhost:3033 is where yt-dlp-webui is exposed
 openid_redirect_url: your-callback-url