I have recently done that and it's actually pretty easy.

• Go to Google Takeout https://takeout.google.com/settings/takeout?pli=1
• Find Google Keep from the list
• Download the zip file with HTML version of keep notes in it

• Use pandoc to convert your html notes into markdown

sudo apt install pandoc

pandoc -f html -t markdown_github-raw_html input.html -o output.md

• And show your converted markdown files' location to pervane:

pervane --dir=/foo/bar/my_keep_notes_folder