Update chat_simpleprompt.cs

Author: achandmsft

docs/guides/text/chat/chat_simpleprompt.cs

@@ -1,5 +1,6 @@
 // SAMPLE: Generate text from a simple prompt
-// GUIDANCE: Instructions to run this code: https://aka.ms/oai/net/start 
+// GUIDANCE: https://platform.openai.com/docs/guides/text?api-mode=chat 
+// HOWTO: Instructions to run this code: https://aka.ms/oai/net/start 
 #:package OpenAI@2.2.*-*
 #:property PublishAot false
 
@@ -8,4 +9,4 @@
 string key = Environment.GetEnvironmentVariable("OPENAI_API_KEY")!;
 ChatClient client = new("gpt-4.1", key);
 ChatCompletion acompletion = client.CompleteChat("Write a one-sentence bedtime story about a unicorn.");
-Console.WriteLine(acompletion.Content[0].Text);
+Console.WriteLine(acompletion.Content[0].Text);