update changelog

Author: Uk1288

CHANGELOG.md

@@ -7,6 +7,7 @@ Experiments are only enabled in alpha releases of Terraform CLI. The following f
 
 - The new command `terraform rpcapi` exposes some Terraform Core functionality through an RPC interface compatible with [`go-plugin`](https://github.com/hashicorp/go-plugin). The exact RPC API exposed here is currently subject to change at any time, because it's here primarily as a vehicle to support the [Terraform Stacks](https://www.hashicorp.com/blog/terraform-stacks-explained) private preview and so will be broken if necessary to respond to feedback from private preview participants, or possibly for other reasons. Do not use this mechanism yet outside of Terraform Stacks private preview.
 - The experimental "deferred actions" feature, enabled by passing the `-allow-deferral` option to `terraform plan`, permits `count` and `for_each` arguments in `module`, `resource`, and `data` blocks to have unknown values and allows providers to react more flexibly to unknown values. This experiment is under active development, and so it's not yet useful to participate in this experiment
+- The new command `terraform stacks` exposes some [Terraform Stack](https://www.hashicorp.com/blog/terraform-stacks-explained) operations through the cli. The available subcommands depend on the stacks plugin implementation. Use `terraform stacks -help` to see available commands.
 
 ## Previous Releases