Clarify publication process

[kwin]

Currently this website is partly broken and not yet leveraged for the official m2e documentation. There is some INFRA work to be done, which is tracked in https://gitlab.eclipse.org/eclipsefdn/helpdesk/-/issues/2171.

After everything is clarified

• This readme should be extended
• The old website repo at https://github.com/eclipse-m2e/m2e-website should be deleted
• A link to this repo should be added to https://github.com/eclipse-m2e/m2e-core/blob/master/CONTRIBUTING.md

[kwin]

It seems that the original MD sources were somehow lost. @fbricon Any idea how the website was generated in the past? According to the readme it was a Jekyll based build (https://github.com/eclipse-m2e/eclipse-m2e.github.io/blob/master/README.md) but I don't see the usual Jekyll metadata and folder structure nor the MD sources...

[fbricon]

So, after some digging I found them:

• jekyll based website is stored in https://github.com/takari/m2eclipse-website. Over 10 years ago, @jvanzyl did reimplement jekyll as a Java app (working surprisingly well), so you just need to run the ./jekyll.sh script that runs a jekyll.jar (no idea where those sources are)
• the generated html site was created in _site/ which itself is a git submodule of the actual (old?) m2e website repo.

Back in the day, you'd make your changes locally, then committed the generated _site submodule so it could then be deployed (automatically IIRC).