[RFE] Build including local gems

[filbranden]

Hi,

This is a request for enhancement, a new feature.

I've been using docker-github-pages to test changes in some of the Ruby components (more specifically, jekyll/github-metadata), but I've been using a dirty hack to put the bits into the container, with this Dockerfile:

FROM starefossen/github-pages:latest
COPY github-metadata/lib/ /usr/local/bundle/gems/jekyll-github-metadata-2.9.4/lib/

I tried to do this in a cleaner way but didn't really find a good way to do so...

Would it be possible to provide a separate Dockerfile (similar to "onbuild" perhaps) that would take additional Ruby Gems from a local repository and use them in the build or upgrade the Gems in the container to those in the local repository? That, together with instructions on how to include additional Gems would be really useful in using this container to develop Jekyll plugins for GitHub pages, without the burden of setting up a local environment for it...

Thanks!
Filipe