Update README for push notification.

[kavi707]

Need to update readme, that how developer can storing push object in database. As follows
GCM:
"push" : {
"notifier" : "google",
"regId" : "APA91bEWIUOEzbsnx3WHwOnrLqYC455p3hlPKU2366pxQJOGsdLdn59rQa6W2_KEF2LbdCNfR9IXQeSAa0XzyKjzIqJ0upWGIpVfUZlC21L7MMfIwBZdAdpk3ru6Yxz7Ksbxqb7vu-Fh2D94NCjPd9GVEYX8di87Ff11yv_300T6zxEb-JfFd3Q"
}

APNS:
"push" : {
"notifier" : "apple",
"regId" : "APA91bEWIUOEzbsnx3WHwOnrLqYC455p3hlPKU2366pxQJOGsdLdn59rQa6W2_KEF2LbdCNfR9IXQeSAa0XzyKjzIqJ0upWGIpVfUZlC21L7MMfIwBZdAdpk3ru6Yxz7Ksbxqb7vu-Fh2D94NCjPd9GVEYX8di87Ff11yv_300T6zxEb-JfFd3Q"
}