Update README.md

Author: leastprivilege

README.md

@@ -1,5 +1,18 @@
 # IdentityModel.AspNetCore.OAuth2Introspection
 
-ASP.NET Core authentication middleware using OAuth 2.0 token introspection
+ASP.NET Core 2 authentication for OAuth 2.0 token introspection
 
 https://tools.ietf.org/html/rfc7662
+
+## Configuration
+
+```csharp
+services.AddAuthentication(OAuth2IntrospectionDefaults.AuthenticationScheme)
+    .AddOAuth2Introspection(options =>
+    {
+        options.Authority = "https://base_address_of_token_service";
+
+        options.ClientId = "client_id_for_introspection_endpoint";
+        options.ClientSecret = "client_secret_for_introspection_endpoint";
+    });
+```