How to install npm package while offline?

I’m working on an offline network and want to install angular-cli using npm.
I have a zip file of angular-cli and using the latest node and npm version.
I’m using the command: npm install ./angular-cli-master to install angular-cli from the folder.
But I keep getting this error telling me I don’t have an internet connection (which is ok).
So how can I install this angular-cli while offline using the zip I downloaded from Github?