The Opsgenie API key, schedule name, and Mattermost webhook URL are read from environment variables. To set these environment variables, you can use the export command in your terminal:

export OPSGENIE_API_KEY=<your_api_key>
export MATTERMOST_WEBHOOK_URL=<your_webhook_url>
export MATTERMOST_API_KEY=<your_api_key>

After that, you can run the project by issuing

go run main.go

or

go run main.go -next-week