title: IConfiguration in Startup.cs
body: <p><code>IConfiguration</code> is automatically added in <code>Startup.ca</code></p>
  <pre><code>    public Startup(IConfiguration configuration)
      {
          conf = configuration;
      }
  </code></pre>
  <p>similarly we can add it to controllers with dependency injection. Now thats an interface, but we can still use its methods like a class(like <code>conf.GetSection</code> as an example). Where and how is the inherited class setup for <code>IConfiguration</code> that we can use its methods that return a value?</p>