Clarify WebGPU browser compat in WebGPUDemo/README.md

Author: MaxDesiatov

WebGPUDemo/README.md

@@ -9,6 +9,13 @@ the Swift SDK in the following command to the version that matches your installe
 swift package --swift-sdk swift-DEVELOPMENT-SNAPSHOT-2025-06-03-a_wasm js --use-cdn
 ```
 
+WebGPU requires a beta or technical preview version of Safari. For recent release versions make sure to enable
+WebGPU feature flag as shown on the screenshot:
+
+<img width="833" alt="Screenshot 2025-06-19 at 10 22 57" src="https://github.com/user-attachments/assets/7d0453ab-da51-4a6e-85da-dc466cf775be" />
+
+See [the WebGPU Implementation Status page](https://github.com/gpuweb/gpuweb/wiki/Implementation-Status) for information about compatibility with other browsers.
+
 Start a HTTP server with eg. `python -m http.server` or `npx serve`, then open
 http://localhost:8000 to view the Swift logo rendered using WebGPU.