Fail to start application - "electron-forge: command not found"

Installing and running using the app using the commands from the README fails.

git clone https://github.com/felixrieseberg/electron-code-editor
cd electron-code-editor
npm install
npm start

Gives me the following error.

> electron-code-editor@1.0.0 start /Users/anders/Apps/electron-code-editor
> electron-forge start

sh: electron-forge: command not found

I have git, node and npm installed. However I do not have electron forge, as it is not stated as a prerequisite. Do I need to install that manually first?

Running this on macOS Sierra (10.12.5) with GIT 2.10.1, NODE 7.9.0 and NPM 4.2.0.