Update README.md to fix the server sample build issue. (#546)

* Update README.md to fix the server sample build issue.

Update README.md to fix the server sample build issue.

* Update README.md

---------

Co-authored-by: Eirik Tsarpalis <eirik.tsarpalis@gmail.com>

Author: Anduin2017

README.md

@@ -166,8 +166,8 @@ public static class MyPrompts
 More control is also available, with fine-grained control over configuring the server and how it should handle client requests. For example:
 
 ```csharp
-using ModelContextProtocol.Protocol.Transport;
-using ModelContextProtocol.Protocol.Types;
+using ModelContextProtocol;
+using ModelContextProtocol.Protocol;
 using ModelContextProtocol.Server;
 using System.Text.Json;
 
@@ -212,9 +212,9 @@ McpServerOptions options = new()
                         throw new McpException("Missing required argument 'message'");
                     }
 
-                    return ValueTask.FromResult(new CallToolResponse()
+                    return ValueTask.FromResult(new CallToolResult
                     {
-                        Content = [new Content() { Text = $"Echo: {message}", Type = "text" }]
+                        Content = [new TextContentBlock { Text = $"Echo: {message}", Type = "text" }]
                     });
                 }