docker-steam-headless/overlay/templates/sunshine/apps.json

{
    "env": {
        "PATH": "$(PATH):$(HOME)\/.local\/bin"
    },
    "apps": [
        {
            "name": "Steam BigPicture",
            "output": "steam.txt",
            "cmd": "",
            "detached": [
                "\/usr\/games\/steam steam:\/\/open\/bigpicture"
            ]
        }
    ]
}