docs: add standardized CONTRIBUTING.md

[John15321]

Summary

This PR adds a standardized CONTRIBUTING.md file that:

• Welcomes new contributors
• Links to the main Flatcar CONTRIBUTING guide
• Provides a section for repo-specific guidelines

This change is part of a batch update across all Flatcar repositories to ensure consistent contribution documentation.

Ref: flatcar/Flatcar#1865

[dongsupark]

I am not sure if we need to add that to this repo, because torcx was deprecated long time ago.
Even LTS 4081.3.x does not have torcx.

Let's hold it and do not merge for now.

[John15321]

My answer here would be the same as for the other one: flatcar/flatcar-ipxe-scripts#6 (comment)

[dongsupark]

Ok, I understand your reasoning.

However, if we continue updating the deprecated repos, maintenance burden would stay like before, and the repos would be potential places for unexpected spams, and we would likely forget reducing the number of repos in the future.

How about trying to archive the repos, i.e. container-linux-config-transpiler, flatcar-ipxe-scripts, ignition, torcx, by gathering votes from maintainers in the mailing list?

[John15321]

Ok, I understand your reasoning.

However, if we continue updating the deprecated repos, maintenance burden would stay like before, and the repos would be potential places for unexpected spams, and we would likely forget reducing the number of repos in the future.

How about trying to archive the repos, i.e. container-linux-config-transpiler, flatcar-ipxe-scripts, ignition, torcx, by gathering votes from maintainers in the mailing list?

I am definitely for it! I remember some time ago we did raise this issue but I do not remember why we did not do it (flatcar/Flatcar#1715)

@dongsupark Do you know if there is a specific voting process for archiving old repos that we should follow?

[dongsupark]

I do not know of a specific process.
Just post suggestions to flatcar-maintainers mailing lists, and wait for weeks for gathering votes.

[John15321]

I do not know of a specific process. Just post suggestions to flatcar-maintainers mailing lists, and wait for weeks for gathering votes.

Yeah I thnk thats the only way. I couldnt find anything in governance. I will do it