Use the composer global command:

composer global require "connorvg/forge-deploy=~1.0"

Make sure to place the ~/.composer/vendor/bin directory in your PATH so the forge-deploy executable is found when you run the forge-deploy command in your terminal.

Once you have installed, you're ready to add deployments:

forge-deploy save [name] [endpoint]

To update a deployment:

forge-deploy update [name] [new-endpoint]

To delete a deployment:

forge-deploy delete [name]

Finally, to deploy:

forge-deploy deploy [name]