Provide System.Composition.TypedParts package readme (#106785)

* Provide System.Composition.TypedParts package readme

* Improve after feedback

src/libraries/System.Composition.TypedParts/src/PACKAGE.md

@@ -0,0 +1,88 @@
+## About
+
+<!-- A description of the package and where one can find more documentation -->
+
+`System.Composition.TypedParts` is part of the Managed Extensibility Framework (MEF) 2.0, a composition library for .NET that enables dependency injection through attributes or conventions.
+
+Provides `ContainerConfiguration` and some extension methods for the Managed Extensibility Framework (MEF).
+
+## Key Features
+
+<!-- The key features of this package -->
+
+* Provides container configuration.
+
+## How to Use
+
+<!-- A compelling example on how to use this package with code, as well as any specific guidelines for when to use the package -->
+
+Register parts from an entire assembly.
+
+```csharp
+using System.Composition;
+using System.Composition.Hosting;
+using System.Reflection;
+
+// Register all parts from the current assembly
+var configuration = new ContainerConfiguration()
+    .WithAssembly(Assembly.GetExecutingAssembly());
+
+using CompositionHost container = configuration.CreateContainer();
+
+var handlers = container.GetExports<IHandler>();
+foreach (var handler in handlers)
+{
+    handler.Handle();
+}
+// HandlerA is handling.
+// HandlerB is handling.
+
+public interface IHandler
+{
+    void Handle();
+}
+
+[Export(typeof(IHandler))]
+public class HandlerA : IHandler
+{
+    public void Handle() => Console.WriteLine("HandlerA is handling.");
+}
+
+[Export(typeof(IHandler))]
+public class HandlerB : IHandler
+{
+    public void Handle() => Console.WriteLine("HandlerB is handling.");
+}
+```
+
+## Main Types
+
+<!-- The main types provided in this library -->
+
+The main types provided by this library are:
+
+* `System.Composition.Hosting.ContainerConfiguration`
+* `System.Composition.CompositionContextExtensions`
+
+## Additional Documentation
+
+<!-- Links to further documentation. Remove conceptual documentation if not available for the library. -->
+
+* [Managed Extensibility Framework (MEF)](https://learn.microsoft.com/dotnet/framework/mef/)
+
+## Related Packages
+
+<!-- The related packages associated with this package -->
+
+* [System.Composition](https://www.nuget.org/packages/System.Composition)
+* [System.Composition.AttributedModel](https://www.nuget.org/packages/System.Composition.AttributedModel)
+* [System.Composition.Convention](https://www.nuget.org/packages/System.Composition.Convention)
+* [System.Composition.Hosting](https://www.nuget.org/packages/System.Composition.Hosting)
+* [System.Composition.Runtime](https://www.nuget.org/packages/System.Composition.Runtime)
+
+## Feedback & Contributing
+
+<!-- How to provide feedback on this package and contribute to it -->
+
+System.Composition.TypedParts is released as open source under the [MIT license](https://licenses.nuget.org/MIT).
+Bug reports and contributions are welcome at [the GitHub repository](https://github.com/dotnet/runtime).

src/libraries/System.Composition.TypedParts/src/System.Composition.TypedParts.csproj

@@ -8,16 +8,10 @@
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
     <UseCompilerGeneratedDocXmlFile>false</UseCompilerGeneratedDocXmlFile>
     <IsPackable>true</IsPackable>
-    <PackageDescription>Provides some extension methods for the Managed Extensibility Framework.
-
-Commonly Used Types:
-System.Composition.CompositionContextExtensions
-System.Composition.Hosting.ContainerConfiguration</PackageDescription>
+    <PackageDescription>Provides container configuration and some extension methods for the Managed Extensibility Framework (MEF).</PackageDescription>
     <!-- TODO https://github.com/dotnet/runtime/issues/90400: Annotate for nullable reference types -->
     <Nullable>disable</Nullable>
     <NoWarn>$(NoWarn);nullable</NoWarn>
-    <!-- TODO: Add package README file: https://github.com/dotnet/runtime/issues/99358 -->
-    <EnableDefaultPackageReadmeFile>false</EnableDefaultPackageReadmeFile>
   </PropertyGroup>
 
   <ItemGroup>