Badly need any examples of how to use this plugin

As posted in [stackoverflow](https://stackoverflow.com/questions/50844549/how-to-set-gcs-metadata-from-jenkins-job-using-metadata-plugin), I would like to upload some files to a GCS bucket using [jenkins GCS plugin](https://wiki.jenkins.io/display/JENKINS/Google+Cloud+Storage+Plugin). How do I set metadata, e.g. mime types and compression on it? There seems to be no docs anywhere about this. Thx!