Add Microsoft.Bcl.Async package.md details

diff --git a/src/libraries/Microsoft.Bcl.AsyncInterfaces/src/PACKAGE.md b/src/libraries/Microsoft.Bcl.AsyncInterfaces/src/PACKAGE.md
index 7a9788f..a4a5af4 100644 (file)
--- a/src/libraries/Microsoft.Bcl.AsyncInterfaces/src/PACKAGE.md
+++ b/src/libraries/Microsoft.Bcl.AsyncInterfaces/src/PACKAGE.md
@@ -1,41 +1,61 @@
 ## About
 
-<!-- A description of the package and where one can find more documentation -->
-
-
+As of C# 8, the C# language has support for producing and consuming asynchronous iterators. The library types in support of those features are available in .NET Core 3.0 and newer as well as in .NET Standard 2.1. This library provides the necessary definitions of those types to support these language features on .NET Framework and on .NET Standard 2.0. This library is not necessary nor recommended when targeting versions of .NET that include the relevant support.
 
 ## Key Features
 
 <!-- The key features of this package -->
 
-*
-*
-*
+* Enables the use of C# async iterators on older .NET platforms
 
 ## 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 -->
 
+```C#
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+
+internal static class Program
+{
+    private static async Task Main()
+    {
+        Console.WriteLine("Starting...");
+        await foreach (var value in GetValuesAsync())
+        {
+            Console.WriteLine(value);
+        }
+        Console.WriteLine("Finished!");
+
+        static async IAsyncEnumerable<int> GetValuesAsync()
+        {
+            for (int i = 0; i < 10; i++)
+            {
+                await Task.Delay(TimeSpan.FromSeconds(1));
+                yield return i;
+            }
+        }
+    }
+}
+```
+
 ## Main Types
 
 <!-- The main types provided in this library -->
 
 The main types provided by this library are:
 
-* ``
-* ``
-* ``
+* `IAsyncEnumerable<T>`
+* `IAsyncEnumerator<T>`
+* `IAsyncDisposable<T>`
 
 ## Additional Documentation
 
 <!-- Links to further documentation. Remove conceptual documentation if not available for the library. -->
 
-* [Conceptual documentation](https://learn.microsoft.com/en-us/dotnet/standard/serialization/**LIBRARYNAME**/overview)
-* [API documentation](https://learn.microsoft.com/en-us/dotnet/api/**LIBRARYNAME**)
-
-## Related Packages
-
-<!-- The related packages associated with this package -->
+* [C# Feature Specification](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-8.0/async-streams)
+* [Walkthrough article](https://learn.microsoft.com/archive/msdn-magazine/2019/november/csharp-iterating-with-async-enumerables-in-csharp-8)
 
 ## Feedback & Contributing