Add governance documentation

GOVERNANCE.md

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+# Governance
+
+`ksef4dev` is a small open-source organization governed by a lightweight **BDFL model** (Benevolent Dictators For Life).
+This document describes how the project is run, who does what, and how decisions are made.
+
+## Roles
+
+### Users
+
+Users are anyone who integrates or uses any `ksef4dev` project. We value their input greatly.
+
+Users are encouraged to:
+
+- Report bugs and unexpected behavior via GitHub Issues.
+- Submit feature requests and share feedback.
+- Help others in Discussions.
+
+### Contributors
+
+Contributors are users who have submitted at least one accepted contribution: a code change, documentation fix, or other improvement.
+They appear in the repository's contributor graph and are tagged as *Contributor* in discussions.
+
+Contributors are encouraged to:
+
+- Follow the contributing guidelines in `CONTRIBUTING.md`.
+- Participate in issue discussions and code reviews.
+- Help triage open issues.
+
+### Maintainers
+
+Maintainers are trusted, active contributors invited by a BDFL.
+They are recognized as *Members* of the `ksef4dev` GitHub organization.
+
+Maintainers can:
+
+- Give binding PR approvals.
+- Merge pull requests that have been approved.
+- Triage and label issues.
+- Participate in governance discussions.
+
+Maintainers are expected to stay reasonably active.
+A maintainer who has been inactive for an extended period of time may be moved to *Emeritus* status after a heads-up from a BDFL.
+
+### BDFL
+
+The project is led by two Benevolent Dictators For Life:
+
+- [@alapierre](https://github.com/alapierre)
+- [@karolbryzgiel](https://github.com/karolbryzgiel)
+
+The BDFLs have joint ownership of the organization and final say on all decisions.
+They share responsibilities equally, and either can act independently for routine matters.
+
+BDFLs can:
+
+- Administer the `ksef4dev` GitHub organization and its repositories.
+- Cut **releases** and manage the release process.
+- Bypass branch protection rules when strictly necessary.
+- Invite and remove Maintainers.
+- Resolve disputes and break deadlocks.
+
+## Becoming a Maintainer
+
+There is no formal application process. Contributors who demonstrate:
+
+- Sustained quality contributions over time,
+- Good judgment in code reviews and issue discussions, and
+- Alignment with the project's goals and values
+
+may be invited to become a Maintainer by a BDFL.
+The invitation is extended privately first.
+Maintainership is a recognition of trust, not a reward for volume of contributions.
+
+## Releases
+
+Only BDFLs are authorized to publish releases.
+Release notes should accurately reflect all changes since the previous release and credit contributors where appropriate.
+
+## Code of Conduct
+
+This project follows the [Contributor Covenant](https://www.contributor-covenant.org/version/3/0/code_of_conduct/).
+Instances of unacceptable behavior may be reported to the BDFLs directly via GitHub or email.
+All reports will be handled with discretion and confidentiality.
+
+## Amendments
+
+This document may be updated at any time by a BDFL.
+Significant changes will be announced in the organization's repository changelog or via a pinned discussion.