Add versioning section

docs/changelog.md

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+# Versions & changelog
+
+
+# Versioning
+
+Our versioning policy follows the [Semantic Versioning specification](https://semver.org/). 
+In our case, given a version `MAJOR.MINOR.PATCH`, we increment the:
+
+* `MAJOR` version when the data model of the Graph changes
+* `MINOR` version when the pipeline (e.g., different deduplication method, different implementation for an enrichment process) or the data sources change
+* `PATCH` version when the graph data are updated
+
+
 # Changelog
-<span className="todo">TODO</span>
+
+This section will document all notable changes for each graph version.
+
+
+## v5.0.0 - [date]
+
+### Added
+
+### Changed
+
+### Deprecated
+
+### Removed
+
+### Fixed