Improve AsyncState README (#4764)

Co-authored-by: Igor Velikorossov <RussKie@users.noreply.github.com>

src/Libraries/Microsoft.AspNetCore.AsyncState/README.md

@@ -1,6 +1,8 @@
 # Microsoft.AspNetCore.AsyncState
 
-This provides the ability to store and retrieve state objects that flow with the current `HttpContext` across asynchronous operations. See `Microsoft.Extensions.AsyncState` for additional information.
+This provides the ability to store and retrieve state objects that flow with the current `HttpContext` across asynchronous operations. See [Microsoft.Extensions.AsyncState](../Microsoft.Extensions.AsyncState/README.md) for additional information.
+
+The lifetime of the shared data is controlled automatically and will be the same as of `HttpContext`.
 
 ## Install the package
 
@@ -28,6 +30,8 @@ The services can be registered using the following method:
 public static IServiceCollection AddAsyncStateHttpContext(this IServiceCollection services)
 ```
 
+Note: When calling `AddAsyncStateHttpContext()` there is no need to also invoke `AddAsyncState()` from the `Microsoft.Extensions.AsyncState` package.
+
 ### Consuming Services
 
 The `IAsyncContext<T>` can be injected wherever async state is needed. For example:

src/Libraries/Microsoft.Extensions.AsyncState/README.md

@@ -1,6 +1,11 @@
 # Microsoft.Extensions.AsyncState
 
-This provides the ability to store and retrieve state objects that flow with the current asynchronous context.
+This provides the ability to store and retrieve objects that flow with the current asynchronous context.
+
+It has a few advantages over using the [`AsyncLocal<T>`](https://learn.microsoft.com/dotnet/api/system.threading.asynclocal-1) class directly:
+- By abstracting the way the ambient data is stored we can use more optimized implementations, for instance when using ASP.NET Core, without exposing these components.
+- Improves the performance by minimizing the number of `AsyncLocal<T>` instances required when multiple objects are shared.
+- Provides a way to manage the lifetime of the ambient data objects.
 
 ## Install the package