Missing ssl in mariabackup option list

refer to the mariabackup option doc page, ssl is missing from
https://mariadb.com/kb/en/library/mariabackup-options/

1. mariabackup --version
   mariabackup based on MariaDB server 10.3.7-MariaDB Linux (x86_64)

1. mariabackup --help | grep ssl
   mariabackup based on MariaDB server 10.3.7-MariaDB Linux (x86_64)
   --ssl Enable SSL for connection (automatically enabled with
   --ssl-ca=name CA file in PEM format (check OpenSSL docs, implies
   --ssl).
   --ssl-capath=name CA directory (check OpenSSL docs, implies --ssl).
   --ssl-cert=name X509 cert in PEM format (implies --ssl).
   --ssl-cipher=name SSL cipher to use (implies --ssl).
   --ssl-key=name X509 key in PEM format (implies --ssl).
   --ssl-crl=name Certificate revocation list (implies --ssl).
   --ssl-crlpath=name Certificate revocation list path (implies --ssl).
   --ssl-verify-server-cert
   ssl TRUE
   ssl-ca /etc/mysql/cc/client.crt
   ssl-capath (No default value)
   ssl-cert /etc/mysql/cc/client.pem
   ssl-cipher (No default value)
   ssl-key /etc/mysql/cc/client.key
   ssl-crl (No default value)
   ssl-crlpath (No default value)
   ssl-verify-server-cert FALSE