Fix documentation for clientutil.BackendConfig change

README.md

@@ -58,7 +58,7 @@ understands the following attributes:
   * `remote_addr_header`: HTTP header to use to obtain the remote
     client address, when the request comes from a trusted forwarder
 * `keystore`: configures the connection to the keystore service
-  * `backend_url`: URL for the keystore service
+  * `url`: URL for the keystore service
   * `tls_config`: client TLS configuration
     * `cert`: path to the client certificate
     * `key`: path to the private key