[Notifier] Document Notifier options in README files

Author: alamirault

README.md

@@ -14,6 +14,40 @@ where:
  - `TOKEN` is your MessageBird token
  - `FROM` is your sender
 
+Adding Options to a Message
+---------------------------
+
+With a MessageBird Message, you can use the `MessageBirdOptions` class to add
+[message options](https://developers.messagebird.com/api/sms-messaging/#send-outbound-sms).
+
+```php
+use Symfony\Component\Notifier\Message\SmsMessage;
+use Symfony\Component\Notifier\Bridge\MessageBird\MessageBirdOptions;
+
+$sms = new SmsMessage('+1411111111', 'My message');
+
+$options = (new MessageBirdOptions())
+    ->type('test_type')
+    ->scheduledDatetime('test_scheduled_datetime')
+    ->createdDatetime('test_created_datetime')
+    ->dataCoding('test_data_coding')
+    ->gateway(999)
+    ->groupIds(['test_group_ids'])
+    ->mClass(888)
+    ->reference('test_reference')
+    ->reportUrl('test_report_url')
+    ->shortenUrls(true)
+    ->typeDetails('test_type_details')
+    ->validity(777)
+    // ...
+    ;
+
+// Add the custom options to the sms message and send the message
+$sms->options($options);
+
+$texter->send($sms);
+```
+
 Resources
 ---------