Update README.md

Author: hawkticehurst

README.md

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 # Webview UI Toolkit Sample Extensions
 
+> [!WARNING]
+> The Webview UI Toolkit for VS Code will be deprecated on January 1, 2025. See the [deprecation announcement](https://github.com/microsoft/vscode-webview-ui-toolkit/issues/561) for more details.
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 This repository contains all the sample extensions for the [Webview UI Toolkit for Visual Studio Code](https://github.com/microsoft/vscode-webview-toolkit).
 
 Each sample is a self-contained extension, and demonstrates some aspect of the toolkit and/or the [Visual Studio Code API](https://code.visualstudio.com/api/references/vscode-api) in relation to the toolkit. You can read, play with, or adapt these samples to create your own extensions.