For everybody else that might need this:
I put the file in this path:
/homeassistant/www/community/threshold-stack/threshold-stack.js
For some reason i dont know, you have to change ā/homeassistant/wwwā to ā/localā when adding the resource to the dashboard (while keeping the file in the same place!!!)
/local/community/threshold-stack/threshold-stack.js