The easiest way to get started with Jdenticon CLI is to use npx to invoke Jdenticon. You don't even have to install the Jdenticon package.
npx jdenticon "value to create icon for" --size 50 --output icon.png
Now go check out icon.png!
The description above assumes that you have Node.js 8.2.0 or later installed on your computer.