Add review policy

Signed-off-by: Benjamin Wang <[email protected]>

Author: ahrtr

Documentation/contributor-guide/review.md

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+# Review policy
+
+To ensure code quality and shared ownership, this review policy applies to all pull requests (PRs).
+
+## Default rule
+
+PRs should get at least two approvals (/lgtm or GitHub review approval) before merging.
+
+Notes:
+- Approvals should come from a maintainer, reviewer, or submodule owner familiar with the relevant code or area.
+- If there’s disagreement, maintainers should discuss and agree before merging.
+
+## Exceptions for Less Impactful PRs
+
+For smaller or low-risk changes — such as:
+
+- Tests
+- CI workflows
+- Documentation
+- Comments
+
+The rule can be relaxed:
+
+- One approval is generally enough.
+
+However:
+
+- If the author is a maintainer, they should still get approval from another maintainer, reviewer, or submodule owner, even for minor changes.