Document the release + contributing process

[tilosp]

@tilosp @J0WI Have you thought about creating a CONTRIBUTING.md file for this repo, where people can learn how to contribute, how things are supposed to work, some basic info about the CI process? That would go a long way, I think :)

Originally posted by @marcelklehr in #863 (comment)

[marcelklehr]

Maybe explaining which files to edit and which are auto-generated by update.sh.

This would definitely be good. :)

@marcelklehr what info about the ci would haven been useful to you? Simply explaining which Dockerfiles get build?

Yeah, I didn't realize that the examples are also built in CI, for example. There's a lot of output in the CI that is difficult to comb through if you don't know what is supposed to happen. An explanation of the general workflow / setup of which scripts are run when, what is happening in CI and perhaps, any tips you have for troubleshooting :)

[joshtrichards]

Moving here instead of the dup issue #2238 initial I created before I remembered this issue already existed:

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Presumably either in the README or a Wiki page (or a bit of page)

• Builds and release process
  • New base images (automatic via Docker's Official Images program I believe)
  • Changes to the image itself (e.g. entrypoint.sh, configs, Dockerfile)
  • New Nextcloud Server versions
  • The build pipeline from this repo and through Docker's Official Image program
  • Tests ran against changes via Docker's Official Image program
  • Special situations
    • Security releases
    • Critical image bug releases
• Contributing
  • How to make changes to the images
  • What to commit
  • Tests that run against PRs

Refs like:

• https://github.com/docker-library/faq?tab=readme-ov-file
• https://github.com/docker-library/bashbrew
• https://github.com/docker-library/official-images
• https://github.com/docker-library/docs?tab=readme-ov-file

[J0WI]

See also https://github.com/docker-library/faq?tab=readme-ov-file#an-images-source-changed-in-git-now-what