Update CHANGELOG.md

CHANGELOG.md

@@ -6,6 +6,7 @@ UPGRADE NOTES:
 * TLS certificate verification for outbound HTTPS requests from Terraform CLI no longer treats the certificate's "common name" as a valid hostname when the certificate lacks any "subject alternative name" entries for the hostname. TLS server certificates must list their hostnames as a "DNS name" in the subject alternative names field. [GH-26357]
 * Outbound HTTPS requests from Terraform CLI now enforce [RFC 8446](https://tools.ietf.org/html/rfc8446)'s client-side downgrade protection checks. This should not significantly affect normal operation, but may result in connection errors in environments where outgoing requests are forced through proxy servers and other "middleboxes", if they have behavior that resembles a downgrade attack. [GH-26357]
 * Terraform's HTTP client code is now slightly stricter than before in HTTP header parsing, but in ways that should not affect typical server implementations: Terraform now trims only _ASCII_ whitespace characters, and does not allow `Transfer-Encoding: identity`. [GH-26357]
+* The `terraform 0.13upgrade` subcommand and the associated upgrade mechanisms are no longer available. Complete the v0.13 upgrade process before upgrading to Terraform v0.14.
 
 ENHANCEMENTS: