Added FCM.deleteInstanceId()

Author: andrehtissot

README.md

@@ -147,6 +147,7 @@ Example:
 - [As its own](#as-its-own)
   - [FCM.clearAllNotifications()](#fcmclearallnotifications)
   - [FCM.createNotificationChannel()](#fcmcreatenotificationchannel)
+  - [FCM.deleteInstanceId()]
   - [FCM.getAPNSToken()](#fcmgetapnstoken)
   - [FCM.getInitialPushPayload()](#fcmgetinitialpushpayload)
   - [FCM.getToken()](#fcmgettoken)
@@ -190,6 +191,13 @@ await FCM.createNotificationChannel({
 });
 ```
 
+##### FCM.deleteInstanceId()
+
+Deletes the InstanceId, revoking all tokens.
+```typescript
+await FCM.deleteInstanceId();
+```
+
 ##### FCM.getAPNSToken()
 
 Gets iOS device's current APNS token.