Improve example for runtime.WithCaptureResponse (#21302)

* Improve example for runtime.WithCaptureResponse

* make linter happy

* fix sentence

sdk/azcore/runtime/examples_test.go

@@ -4,14 +4,22 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT License.
 
-package runtime
+package runtime_test
 
 import (
 	"context"
 	"net/http"
+
+	"github.com/Azure/azure-sdk-for-go/sdk/azcore/runtime"
 )
 
 func ExampleWithCaptureResponse() {
 	var respFromCtx *http.Response
-	WithCaptureResponse(context.Background(), &respFromCtx)
+	ctx := context.TODO()
+	ctx = runtime.WithCaptureResponse(ctx, &respFromCtx)
+	// make some client method call using the updated context
+	// resp, err := client.SomeMethod(ctx, ...)
+	// *respFromCtx contains the raw *http.Response returned during the client method call.
+	// if the HTTP transport didn't return a response due to an error then *respFromCtx will be nil.
+	_ = ctx
 }