Clarify filemounted crl usage (#3331)

Signed-off-by: Faseela K <[email protected]>

Author: kfaseela

networking/v1alpha3/destination_rule.pb.go

@@ -923,7 +923,8 @@ message ClientTLSSettings {
   // to use in verifying a presented server certificate. `CRL` is a list of certificates
   // that have been revoked by the CA (Certificate Authority) before their scheduled expiration date.
   // If specified, the proxy will verify if the presented certificate is part of the revoked list of certificates.
-  // If omitted, the proxy will not verify the certificate against the `crl`.
+  // If omitted, the proxy will not verify the certificate against the `crl`. Note that if `credentialName` is set,
+  // `CRL` cannot be specified using `caCrl`, rather it has to be specified inside the credential.
   string ca_crl = 9;
 }