(chore) prepare for release v2.0.0

Author: epwalsh

CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+## [v2.0.0](https://github.com/allenai/OLMo-core/releases/tag/v2.0.0) - 2025-03-12
+
 This major release introduces a few breaking changes. We've provided more information here: [OLMo-core v2 design and upgrade guide](https://docs.google.com/document/d/1LvANhNzA-MdtiD2pLniLTqB9wxSSuqY435WuJIADeFM/edit?usp=sharing).
 
 ### Added