add HttpClient extension

Author: AntPolkanov

docs/quickstart/server.mdx

@@ -1484,6 +1484,23 @@ When creating the `ApplicationHostBuilder`, ensure you use `CreateEmptyApplicati
 This code sets up a basic console application that uses the Model Context Protocol SDK to create an MCP server with standard I/O transport.
 
 ### Weather API helper functions
+
+Create an extension class for `HttpClient` which helps simplify JSON request handling:
+
+```csharp
+using System.Text.Json;
+
+internal static class HttpClientExt
+{
+    public static async Task<JsonDocument> ReadJsonDocumentAsync(this HttpClient client, string requestUri)
+    {
+        using var response = await client.GetAsync(requestUri);
+        response.EnsureSuccessStatusCode();
+        return await JsonDocument.ParseAsync(await response.Content.ReadAsStreamAsync());
+    }
+}
+```
+
 Next, define a class with the tool execution handlers for querying and converting responses from the National Weather Service API:
 
 ```csharp