[docs] release notes for PR 3958

Missing docs for: dotnet#3958

Documentation/release-notes/3958.md

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+### Breaking change for `.exe` files
+
+Since Xamarin.Android 9.4, `.exe` files are not considered at *build time* and are not included in the final APK for Xamarin.Android applications:
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+https://github.com/xamarin/xamarin-android/commit/e390702773365ffe3da975181d0aa398d42731d0
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+To improve startup performance, Xamarin.Android no longer probes for `.exe` files at *runtime*. A standard project type such as a `netstandard` library, Xamarin.Android class library, Xamarin.Android binding library, a [shared project][shared_project], or even a portable class library will not have a problem. Consider using one of the support project types moving forward.
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+[shared_project]: https://docs.microsoft.com/xamarin/cross-platform/app-fundamentals/shared-projects