A nodejs must be installed prior to omg utility installation: https://nodejs.org/en/
After that, in your terminal run following command: npm i -g @ombori/ga-cli. That will install omg utility.
After utility is installed, you need to put an authorisation token into a config file:
OS X:echo AUTH_TOKEN=your-token >> ~/.gridapprc
Windows:
echo AUTH_TOKEN=your-token >> %HOME%/.gridapprc
The token can be obtained from ombori.