Update ns-System.Collections.Immutable.xml (#9398)

xml/ns-System.Collections.Immutable.xml

@@ -9,28 +9,11 @@
 With immutable collections, you can:
 
 - Share a collection in a way that its consumer can be assured that the collection never changes.
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 - Provide implicit thread safety in multi-threaded applications (no locks required to access collections).
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 - Follow functional programming practices.
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 - Modify a collection during enumeration, while ensuring that the original collection does not change.
 
-The immutable collection classes are available with .NET Core and .NET 5+, however they're not part of the core class library distributed with .NET Framework. They're available starting with .NET Framework 4.5 via NuGet.
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-To install the immutable collections via NuGet:
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-1. Open your project in Visual Studio and choose **Manage NuGet Packages** from the **Project** menu.
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-2. Optionally, select the **Include prerelease** checkbox.
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-   This option gives you access to new prerelease versions of the immutable classes, as they become available.
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-3. Use the **Search** box to locate the **System.Collections.Immutable** package.
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-4. In the left pane, select the **System.Collections.Immutable** package. In the right pane, select the desired version and then choose Install.
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-The installation steps described above are for Visual Studio 2015. For other versions of Visual Studio, the steps might be slightly different because of differences in the user interface (UI).
+The immutable collection classes are available as part of the core .NET libraries, however they're not part of the core class library distributed with .NET Framework. For .NET Framework 4.6.2 and later apps, the classes are available through NuGet packages.
 
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