Add changelog

changelog_unreleased/cli/17151.md

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+#### Support experimental CLI (#17151 by @fisker)
+
+You may already heard or used our new [performance improved CLI](https://prettier.io/blog/2023/11/30/cli-deep-dive). From prettier main, you can use it without installing unstable v4 version.
+
+1. Install `@prettier/cli` package
+
+   ```sh
+   yarn add prettier @prettier/cli --dev
+   ```
+
+1. Run Prettier with environment variable `PRETTIER_EXPERIMENTAL_CLI=1`
+
+   ```sh
+   PRETTIER_EXPERIMENTAL_CLI=1 prettier . --check
+   ```