Fix tls_config -> tls

README.md

@@ -108,7 +108,7 @@ default from */etc/keystore/dovecot.yml*:
   * `url`: URL for the keystore service
   * `sharded`: if true, requests to the keystore service will be
     partitioned according to the user's *shard* attribute
-  * `tls_config`: client TLS configuration
+  * `tls`: client TLS configuration
     * `cert`: path to the client certificate
     * `key`: path to the private key
     * `ca`: path to the CA used to validate the server