note time_to_live

Author: erlangparasu

readme.md

@@ -102,6 +102,9 @@ fcm()
     ->send();
 ```
 
+**NOTE**: By default, Firebase server will queue your notification in 4 weeks. You could change this behavior by setting `->timeToLive(value_in_seconds)`. For example snippet above "->timeToLive(0)" will skip the queue, the target device (eg. android) must be online when the notification arive, otherwhise the target device will not receive the notification.
+
+
 If You want to send a FCM to topic, use method toTopic(\$topic) instead to() :
 
 ```php