Create GOVERNANCE.md

As per request from @comcon1, and as discussed with @ohsOllila and @korbinib, I have created this minimal governance document.

Author: markussmiettinen

GOVERNANCE.md

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+# Governance
+
+FAIRMD is governed by a simple principle: Work together respectfully and pragmatically.
+
+## How we work
+
+- Don't be a jerk.
+- Treat other contributors with respect.
+- Discuss issues openly and aim for consensus.
+
+## How decisions are made
+
+Most decisions are made through discussion and consensus among contributors and maintainers.
+
+If consensus cannot be reached, the project founders (@ohsOllila, @markussmiettinen) make the final decision.
+
+## Final note
+
+This governance model is intentionally lightweight. It exists to support collaboration, not bureaucracy.