Allow prebuilding image without a Dockerfile

[joshspicer]

resolves #106

[joshspicer]

Dev Container:

// For format details, see https://aka.ms/devcontainer.json. For config options, see the
// README at: https://github.com/devcontainers/templates/tree/main/src/debian
{
        "name": "Debian",
        // Or use a Dockerfile or Docker Compose file. More info: https://containers.dev/guide/dockerfile
        "image": "mcr.microsoft.com/devcontainers/base:bullseye"

        // Features to add to the dev container. More info: https://containers.dev/features.
        // "features": {},

        // Use 'forwardPorts' to make a list of ports inside the container available locally.
        // "forwardPorts": [],

        // Configure tool-specific properties.
        // "customizations": {},

        // Uncomment to connect as root instead. More info: https://aka.ms/dev-containers-non-root.
        // "remoteUser": "root"
}

[alexdima]

Nice!