Added readme contents for IoC

README.md

@@ -34,6 +34,8 @@ Table of contents:
         - [Flag clubbing](#flag-clubbing)
 - [Exception handling](#exception-handling)
 - [Dependency Injection](#dependency-injection)
+    - [Autofac](#autofac)
+    - [Microsoft](#microsoft)
 
 ## Installation
 
@@ -915,4 +917,90 @@ catch(MyBusinessException ex)
 
 ## Dependency Injection
 
-Coming soon...
+Let's say your app uses a service :
+
+```c#
+public interface IService
+{
+    int GetValue();
+}
+
+public class Service : IService
+{
+    public int GetValue()
+    {
+        return 4;
+    }
+}
+```
+
+Without dependency injection, app will have to create an instance of `Service` manually:
+
+```c#
+public class App
+{
+    public void PrintServiceValue()
+    {
+        IService service = new Service();
+        Console.WriteLine(service.GetValue().ToString());
+    }
+}
+```
+
+This looks simple now but because the `Service` class constructor doesn't have any construtor parameters but if it had, it would have been difficult for `App` to create the instance of `Service`.
+
+Another reason why you might want to use dependency injection is testable code. This is how `App` looks like with "Property injection"
+
+```c#
+public class App
+{
+    public IService Service {get;set;}
+
+    public void PrintServiceValue()
+    {
+        Console.WriteLine(Service.GetValue().ToString());
+    }
+}
+```
+
+The benefit here is that you can mock IService and just test the behaviour of `App` without worrying about `Service` class.
+
+CommandDotNet supports two IoC frameworks - Autofac & Microsoft
+
+### Autofac
+
+In order to use autofac, you need to install an additional integration nuget package : https://www.nuget.org/packages/CommandDotNet.IoC.Autofac/
+
+This how you can use the package:
+
+```c#
+static int Main(string[] args)
+{
+    ContainerBuilder containerBuilder = new ContainerBuilder();
+    containerBuilder.RegisterType<Service>().As<IService>();
+    IContainer container = containerBuilder.Build();
+
+    AppRunner<ServiceApp> appRunner = new AppRunner<ServiceApp>().UseAutofac(container);
+
+    return appRunner.Run(args);
+}
+```
+
+### Microsoft
+
+In order to use microsoft dependency injection, you need to install an additional integration nuget package : https://www.nuget.org/packages/CommandDotNet.IoC.MicrosoftDependencyInjection/
+
+This how you can use the package:
+
+```c#
+static int Main(string[] args)
+{
+    IServiceCollection serviceCollection = new ServiceCollection();
+    serviceCollection.AddSingleton<IService, Service>();
+    IServiceProvider serviceProvider = serviceCollection.BuildServiceProvider();
+
+    AppRunner<ServiceApp> appRunner = new AppRunner<ServiceApp>().UseMicrosoftDependencyInjection(serviceProvider)
+
+    return appRunner.Run(args);
+}
+```