Update CHANGELOG.md to specify important changes

Author: Vadorequest

CHANGELOG.md

@@ -1,6 +1,16 @@
 CHANGELOG
 ===
 
-Please visit [our releases page](../../releases).
+## Migrating (breaking changes)
 
-Each release is automatic, using the workflow [`.github/workflows/auto-git-release.yml`](/blob/main/.github/workflows/auto-git-release.yml).
+### v3
+No breaking changes.
+
+- [v3 uses Node16 instead of node12](https://github.com/UnlyEd/github-action-store-variable/releases/tag/v3.0.0).
+
+### v2
+_I don't remember._
+
+---
+
+Please visit [our releases page](../../releases) for more details.