Lightning CLI relies on Heroku Toolbelt. Make sure that you have the heroku command installed correctly before attempting to use Lightning CLI. More information about Heroku Toolbelt is available here:
https://devcenter.heroku.com/articles/getting-started-with-nodejs#set-up
After getting Heroku Toolbelt up and running, install the Lightning CLI plugin using the following command:
heroku plugins:install salesforce-lightning-cli
Once installed, the plugin is updated whenever you update the Heroku Toolbelt using the heroku update command. Run the update command every week or so to make sure you’ve got the latest Lightning CLI rules.