Update modern .NET C# UWP app documentation

[tommcdon]

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Learn Build status updates of commit f2f736f:

✅ Validation status: passed

File	Status	Preview URL	Details
uwp/dotnet-native/getting-started-with-net-native.md	✅Succeeded
uwp/dotnet-native/index.md	✅Succeeded
uwp/dotnet-native/modernize-uwp-apps-with-dotnet.md	✅Succeeded
uwp/get-started/create-a-hello-world-app-xaml-universal.md	✅Succeeded
uwp/get-started/universal-application-platform-guide.md	✅Succeeded

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PRMerger Results

Issue	Description
Added File(s)	This PR contains added files. New files require human review.
File Change Percent	This PR contains file(s) with more than 30% file change.
Index File	This PR contains a change to the index file.