[Notifier] Document Notifier options in README files

Author: alamirault

GatewayApiOptions.php

@@ -33,7 +33,7 @@ public function getRecipientId(): ?string
     /**
      * @return $this
      */
-    public function class(int $class): static
+    public function class(string $class): static
     {
         $this->options['class'] = $class;
 

README.md

@@ -16,6 +16,31 @@ where:
 
 See your account info at https://gatewayapi.com
 
+Adding Options to a Message
+---------------------------
+
+With a GatewayApi Message, you can use the `GatewayApiOptions` class to add
+[message options](https://gatewayapi.com/docs/apis/rest/).
+
+```php
+use Symfony\Component\Notifier\Message\SmsMessage;
+use Symfony\Component\Notifier\Bridge\GatewayApi\GatewayApiOptions;
+
+$sms = new SmsMessage('+1411111111', 'My message');
+
+$options = (new GatewayApiOptions())
+    ->class('standard')
+    ->callbackUrl('https://my-callback-url')
+    ->userRef('user_ref')
+    // ...
+    ;
+
+// Add the custom options to the sms message and send the message
+$sms->options($options);
+
+$texter->send($sms);
+```
+
 Resources
 ---------
 

Tests/GatewayApiOptionsTest.php

@@ -19,12 +19,12 @@ class GatewayApiOptionsTest extends TestCase
     public function testGatewayApiOptions()
     {
         $gatewayApiOptions = (new GatewayApiOptions())
-            ->class(123)
+            ->class('test_class')
             ->callbackUrl('test_callback_url')
             ->userRef('test_user_ref');
 
         self::assertSame([
-            'class' => 123,
+            'class' => 'test_class',
             'callback_url' => 'test_callback_url',
             'userref' => 'test_user_ref',
         ], $gatewayApiOptions->toArray());