You know, I’m not 100% sure about documentation on that! But if you have general understanding of working with the machine through terminal, then this is what you’ll want to do;
Ssh in to the norns by looking at the IP address (key 2 on the home screen) and typing
ssh we@IP_ADDRESS_HERE
Then, cd ~/dust/code
This will bring you to the code directory.
Then, look at the github page of the script you want. There will be a green button to potentially download the code; but there will also be a link. Copy the link.
Then enter this in to your terminal;
git clone DIRECTORY_YOU_COPIED
Hit enter. It should download. Open your scripts folder on your norns and you should see it there!

Edit; this is all assuming you have a Mac, my bad. It should be relatively similar for a PC, but with its own terminal commands