Use image: silex/emacs:master-alpine-dev?
I've just switched to this image, mostly because it contains Git as well, which I find very useful to introspect the repository. (This is GitLab after all!) For instance, I can use custom Elisp functions to query the commit dates of my blog articles.
I thought I'd just let you know, and if you don't consider switching, maybe mention it in the README?