update readme

Author: Mohamad Fadhil

README.md

@@ -627,6 +627,7 @@ the client used to send the request.
 | `client.identity-aware-proxy.audience` | The Identity-Aware-Proxy audience. (client-id of the IAP oauth2 credential)   | required `""`   |
 | `client.tls.certificate-file`          | Path to a client certificate (in PEM format) for mTLS configurations.         | `""`            |
 | `client.tls.private-key-file`          | Path to a client private key (in PEM format) for mTLS configurations.         | `""`            |
+| `client.tls.ca-file`                   | Path to a root CA (in PEM format) for mTLS configurations.                    | Optional `""`   |
 | `client.tls.renegotiation`             | Type of renegotiation support to provide. (`never`, `freely`, `once`).        | `"never"`       |
 | `client.network`                       | The network to use for ICMP endpoint client (`ip`, `ip4` or `ip6`).           | `"ip"`          |
 | `client.tunnel`                        | Name of the SSH tunnel to use for this endpoint. See [Tunneling](#tunneling). | `""`            |