- updates getting started for new authentication provider

Author: baywet

README.md

@@ -28,10 +28,11 @@ For an example of how to get an authentication provider, see [choose a Microsoft
 
 ```Ruby
 require "microsoft_kiota_authentication_oauth"
+require "microsoft_graph_core"
 
 context = MicrosoftKiotaAuthenticationOauth::ClientCredentialContext.new("<the tenant id from your app registration>", "<the client id from your app registration>", "<the client secret from your app registration>")
 
-authentication_provider = MicrosoftKiotaAuthenticationOauth::OAuthAuthenticationProvider.new(context, nil, ["Files.Read"])
+authentication_provider = MicrosoftGraphCore::Authentication::OAuthAuthenticationProvider.new(context, nil, ["Files.Read"])
 ```
 
 ### 2.3 Get a Graph Service Client and Adapter object