Update README.md

Author: mediumTaj

src/IBM.WatsonDeveloperCloud.NaturalLanguageClassifier.v1/README.md

@@ -24,7 +24,20 @@ IBM Watson™ Natural Language Classifier can help your application understand t
 You can create and train a classifier in less than 15 minutes.
 
 #### Instantiating and authenticating the service
-Before you can send requests to the service it must be instantiated and credentials must be set.
+Before you can send requests to the service it must be instantiated and api key or access token must be set.
+```cs
+TokenOptions tokenOptions = new TokenOptions()
+{
+    IamApiKey = "<iam-apikey>",
+    IamAccessToken = "<iam-access-token>",
+    IamUrl = "<service-endpoint>"
+};
+
+var _naturalLanguageClassifierService = new NaturalLanguageClassifierService(tokenOptions);
+
+```
+
+You can also authenticate using username and password.
 ```cs
 // create a Natural Language Classifier Service instance
 NaturalLanguageClassifierService _naturalLanguageClassifierService = new NaturalLanguageClassifierService();