Add alternative Docker image to documentation

[paddy-hack]

I've been "maintaining" an Alpine Linux-based nikola Docker image for a while now (since 2016 :wink:) over at GitLab.com, see paddy-hack/nikola. Maintenance runs mostly on auto-pilot and checks for new releases on a weekly basis. The image is tested using the demo site and only published when the test(s) pass.

BTW, this image is used by the nikola GitLab Pages example.

Seeing that the Getting Started - Docker section mentions an image that has not been updated since mid August 2021 (and doesn't link to the Dockerfile used to build it) as well as an alternative that requires building the image yourself (rather than just pulling), I figured I'd mention mine in case you want to update the documentation.

[Kwpolska]

Thanks, I updated the docs to point to your image (and also improved some other stale things in the getting-started document along the way).

[paddy-hack]

Thanks for the quick follow-up.

[paddy-hack]

Thanks for the quick follow-up.