docs: Updated README>

README.md

@@ -16,7 +16,24 @@
 ```csharp
 using Tavily;
 
-using var client = new TavilyClient(apiKey);
+var apiKey =
+    Environment.GetEnvironmentVariable("TAVILY_API_KEY") ??
+    throw new AssertInconclusiveException("TAVILY_API_KEY environment variable is not found.");
+
+using var client = new TavilyClient();
+
+SearchResponse searchResponse = await client.SearchAsync(
+    apiKey: apiKey,
+    query: "Who is Leo Messi?");
+
+foreach (var result in searchResponse.Results)
+{
+    Console.WriteLine($"Title: {result.Title}");
+    Console.WriteLine($"Content: {result.Content}");
+    Console.WriteLine($"Score: {result.Score}");
+    Console.WriteLine($"Url: {result.Url}");
+    Console.WriteLine();
+}
 ```
 
 ## Support