Specify in docs what to do with standard logger.
// logger := logrus.New()
// logger.SetFormatter(nrlogrusplugin.ContextFormatter{})
//
+// or if you are using the logrus standard logger
+//
+// logrus.SetFormatter(nrlogrusplugin.ContextFormatter{})
+//
// The logger will now look for a newrelic.Transaction inside its context and
// decorate logs accordingly. Therefore, the Transaction must be added to the
// context and passed to the logger. For example, this logging call
