docs: add raw responses to readme

Author: stainless-app[bot]

README.md

@@ -103,6 +103,29 @@ To send a request to the Orb API, build an instance of some `Params` class and p
 
 For example, `client.Customers.Create` should be called with an instance of `CustomerCreateParams`, and it will return an instance of `Task<Customer>`.
 
+## Raw responses
+
+The SDK defines methods that deserialize responses into instances of C# classes. However, these methods don't provide access to the response headers, status code, or the raw response body.
+
+To access this data, prefix any HTTP method call on a client or service with `WithRawResponse`:
+
+```csharp
+var response = await client.WithRawResponse.Customers.Create(parameters);
+var statusCode = response.Message.StatusCode;
+var headers = response.Message.Headers;
+```
+
+For non-streaming responses, you can deserialize the response into an instance of a C# class if needed:
+
+```csharp
+using System;
+using Orb.Models.Customers;
+
+var response = await client.WithRawResponse.Customers.Create(parameters);
+Customer deserialized = await response.Deserialize();
+Console.WriteLine(deserialized);
+```
+
 ## Error handling
 
 The SDK throws custom unchecked exception types: