Convert a Markdown text file into a Google Document using Appscript?

One suggestion: use Pandoc to convert Markdown to docx, then import to Google Docs using the Google Drive API.

You can also accomplish this using the Google Drive web interface:

1. Convert markdown to ODT (or some other intermediate) using pandoc: pandoc MyFile.md -f markdown -t odt -s -o MyFile.odt
2. Move the ODT file into your Google Drive folder.
3. Right-click the ODT file (in the web version of Drive) and press “Open With -> Google Docs”.
4. Google Drive will now create a new Google Doc, with contents matching the ODT file, and open it for you.