There’s an updated version of the conversion script that allows a lot of awesome functionality available at https://github.com/lmmx/gdocs2md-…

The GDocs menu now says “Tools > Script Editor”, and to run the script you want to select your “ConvertToMarkdown” function in the toolbar dropdown, push the “play” button, auth with your google account, and then you’ll get the markdown emailed to you.

This script doesn't store the converted document in Drive but rather emails it to you as an attachment. Just a note.