Update README.md

Author: mediumTaj

src/IBM.WatsonDeveloperCloud.LanguageTranslator.v2/README.md

@@ -23,7 +23,19 @@ PM > Install-Package IBM.WatsonDeveloperCloud.LanguageTranslator.v2
 Select a domain, then identify or select the language of text, and then translate the text from one supported language to another.
 
 #### 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 _languageTranslator = new LanguageTranslator(tokenOptions, "<version-date>");
+```
+
+Services created before 2018-06-15 are authenticated using username and password..
 ```cs
 // create a Language Translator Service instance
 LanguageTranslationService _languageTranslator = new LanguageTranslationService();