Adding Microsoft.Extensions.ObjectPool.DependencyInjection readme file (

#4608)

src/Libraries/Microsoft.Extensions.ObjectPool.DependencyInjection/README.md

@@ -1 +1,94 @@
-README
+# Microsoft.Extensions.ObjectPool.DependencyInjection
+
+This provides the ability to retrieve pooled instances that can be initialized using dependency injection.
+
+## Install the package
+
+From the command-line:
+
+```dotnetcli
+dotnet add package Microsoft.Extensions.ObjectPool.DependencyInjection
+```
+
+Or directly in the C# project file:
+
+```xml
+<ItemGroup>
+  <PackageReference Include="Microsoft.Extensions.ObjectPool.DependencyInjection" Version="[CURRENTVERSION]" />
+</ItemGroup>
+```
+
+## Usage Example
+
+### Registering Pools
+
+The object pools can be registered using the following methods:
+
+```csharp
+    public static IServiceCollection AddPooled<TService>(this IServiceCollection services, Action<DependencyInjectionPoolOptions>? configure = null)
+
+    public static IServiceCollection AddPooled<TService, TImplementation>(this IServiceCollection services, Action<DependencyInjectionPoolOptions>? configure = null)
+```
+
+For example:
+
+```csharp
+var builder = WebApplication.CreateBuilder(args);
+
+builder.Services.AddSingleton<MyService>();
+builder.Services.AddPooled<MyPooledClass>();
+
+var app = builder.Build();
+```
+
+### Consuming Pools
+
+Once registered, pools can be resolved using dependency injection. For example:
+
+```csharp
+var pool = context.RequestServices.GetRequiredService<ObjectPool<MyPooledClass>>();
+
+var obj = pool.Get();
+
+// Use the pooled object ...
+
+pool.Return(obj);
+```
+
+Pooled instances will be resolved from the root dependency injection container and can only
+use singleton dependencies.
+
+Pooled instances can implement `Microsoft.Extensions.ObjectPool.IResettable` in order to
+be initialized when they are returned to the pool.
+
+```csharp
+public class MyPooledClass : IResettable
+{
+    private MyService _myService;
+
+    public MyPooledClass(MyService myService)
+    {
+        _myService = myService;
+    }
+
+    public bool TryReset()
+    {
+        // Clean instance here
+        return true;
+    }
+}
+```
+
+## Options
+
+The `DependencyInjectionPoolOptions.Capacity` property is used to configure the maximum capacity of each pool. The default value is `1024`.
+
+This value can also be set during the pool registration:
+
+```csharp
+builder.Services.AddPooled<MyPooledClass>(options => options.Capacity = 64);
+```
+
+## Feedback & Contributing
+
+We welcome feedback and contributions in [our GitHub repo](https://github.com/dotnet/extensions).