Update README.md

Author: shg8

README.md

@@ -17,6 +17,7 @@ with support for warp-level primitives (subgroups).
 * [Windows](https://github.com/shg8/3DGS.cpp/releases/download/nightly/vulkan_splatting_viewer-windows-latest-amd64-nightly)
 * [macOS (arm64)](https://github.com/shg8/3DGS.cpp/releases/download/nightly/vulkan_splatting_viewer-macos-14-arm64-nightly)
 * [Linux](https://github.com/shg8/3DGS.cpp/releases/download/nightly/vulkan_splatting_viewer-ubuntu-latest-amd64-nightly)
+* iOS, iPad OS, visionOS (as an iPad app) on [TestFlight](https://testflight.apple.com/join/0WzabeP7)
 
 ## Command Line Usage