Add example file stream usage in USE_CASES.md

USE_CASES.md

@@ -28,10 +28,11 @@ namespace Example
     {
         private static void Main()
         {
-            Execute().Wait();
+            ExecuteManualAttachmentAdd().Wait();
+            ExecuteStreamAttachmentAdd().Wait();
         }
 
-        static async Task Execute()
+        static async Task ExecuteManualAttachmentAdd()
         {
             var apiKey = Environment.GetEnvironmentVariable("NAME_OF_THE_ENVIRONMENT_VARIABLE_FOR_YOUR_SENDGRID_KEY");
             var client = new SendGridClient(apiKey);
@@ -45,6 +46,23 @@ namespace Example
             msg.AddAttachment("file.txt", file);
             var response = await client.SendEmailAsync(msg);
         }
+
+        static async Task ExecuteStreamAttachmentAdd()
+        {
+            var apiKey = Environment.GetEnvironmentVariable("NAME_OF_THE_ENVIRONMENT_VARIABLE_FOR_YOUR_SENDGRID_KEY");
+            var client = new SendGridClient(apiKey);
+            var from = new EmailAddress("[email protected]");
+            var subject = "Subject";
+            var to = new EmailAddress("[email protected]");
+            var body = "Email Body";
+            var msg = MailHelper.CreateSingleEmail(from, to, subject, body, "");
+
+            using (var fileStream = File.OpenRead("/Users/username/file.txt"))
+            {
+                msg.AddAttachment("file.txt", fileStream);
+                var response = await client.SendEmailAsync(msg);
+            }
+        }
     }
 }
 ```
@@ -656,4 +674,4 @@ Find more information about all of SendGrid's whitelabeling realated doucmentati
 
 You can find documentation for how to view your email statistics via the UI [here](https://app.sendgrid.com/statistics) and via API [here](https://github.com/sendgrid/sendgrid-csharp/blob/master/USAGE.md#stats).
 
-Alternatively, we can post events to a URL of your choice via our [Event Webhook](https://sendgrid.com/docs/API_Reference/Webhooks/event.html) about events that occur as SendGrid processes your email.
+Alternatively, we can post events to a URL of your choice via our [Event Webhook](https://sendgrid.com/docs/API_Reference/Webhooks/event.html) about events that occur as SendGrid processes your email.