Update changelog.md

changelog.md

@@ -4,6 +4,10 @@ Notice: All 1.7.x changed are present in 2.0.x aswell
 - instance.createAssociationInstance functionality added [#1213](https://github.com/sequelize/sequelize/pull/1213)
 - fixes a few bugs with transactions in regards to associations
 
+### Backwards compatability changes
+- Hooks are no longer passing value hashes. Instead, they are now passing instances of the model.
+- Hook callbacks no longer take two arguments (previously: `err, newValues`). They only take the error argument since values can be changed directly on the model instance.
+
 # v1.7.0-beta8
 - max()/min() now supports dates [#1200](https://github.com/sequelize/sequelize/pull/1200)
 - findAndCountAll now supports the include option