Docs: device/push token instructions in docs

[redolent]

Hi y'all,

If anyone could be so generous as to update the documentation:
https://github.com/phonegap/phonegap-plugin-push/blob/master/docs/API.md#pushsubscribetopic-successhandler-errorhandler

Please add a bit about how to obtain the push token id! Thank you so much!

[redolent]

Hmm... It seems that push.on('registration', ... ); is not being called, could be my fault. :(

The code I am using is:

var push = PushNotification.init({
    ios:{
      sound:      true,
    }
});
push.on('registration', function(data){
    log("registration", JSON.stringify(_.toArray(arguments)));
});
push.on('notification', function(data){
    log("notification", JSON.stringify(_.toArray(arguments)));
});
push.on('error', function(e){
    log("error", JSON.stringify(_.toArray(arguments)));
});
push.subscribe('messages', function(){
    log("subscribe success", JSON.stringify(_.toArray(arguments)));
}, function(){
    log("subscribe error", JSON.stringify(_.toArray(arguments)));
});

[redolent]

Okay, I debugged the code, it's working fine. Would it be alright if I updated the documentation to include the word "token"?