Update README with usage

README.md

@@ -126,10 +126,10 @@ sender.send(message, { registrationTokens: registrationTokens }, 10, function (e
   else    console.log(response);
 });
 
-// Q: I need to remove all "bad" token from my database, how do I do that? 
+// Q: I need to remove all "bad" token from my database, how do I do that?
 //    The results-array does not contain any tokens!
 // A: The array of tokens used for sending will match the array of results, so you can cross-check them.
-sender.send(message, { registrationTokens: registrationTokens }, function (err, response) {  
+sender.send(message, { registrationTokens: registrationTokens }, function (err, response) {
   var failed_tokens = registrationTokens.filter((token, i) => response[i].error != null);
   console.log('These tokens are no longer ok:', failed_tokens);
 });
@@ -167,6 +167,7 @@ This is due to [a restriction](https://firebase.google.com/docs/cloud-messaging/
 |dryRun|Optional, JSON boolean|This parameter, when set to true, allows developers to test a request without actually sending a message.|
 |data|Optional, JSON object|This parameter specifies the custom key-value pairs of the message's payload.|
 |notification|Optional, JSON object|This parameter specifies the predefined, user-visible key-value pairs of the notification payload. See "Notification payload option table" below for more details.|
+|fcm_options|Optional, JSON object|This parameter is used to pass FCM specific options as outlined (here)[https://firebase.google.com/docs/reference/fcm/rest/v1/projects.messages#FcmOptions]|
 
 ## Notification usage