Updated docs

CHANGELOG.md

@@ -2,10 +2,15 @@
 
 All notable changes to `laravel-eloquent-state-machines` will be documented in this file
 
+## v4.0.0 - 2021-02-12
+
+- Added `changed_attributes` field in `state_histories` to record model old/new 
+  values during transition (**Breaking change**)
+
 ## v3.0.0 - 2021-02-10
 
 - Added `beforeTransitionHooks`
-- **Breaking Change**: Renamed `transitionHooks` to `afterTransitionHooks` and changed arguments for callbacks
+- Renamed `transitionHooks` to `afterTransitionHooks` and changed arguments for callbacks (**Breaking Change**)
 - Refactored tests
 
 ## v2.3.0 - 2020-01-26

README.md

@@ -346,6 +346,29 @@ $salesOrder->status()->snapshotWhen('approved')->responsible;
 
 ## Advanced Usage
 
+### Tracking Attribute Changes
+
+When `recordHistory()` is active, model state transitions are recorded in the `state_histories` table. Each transition
+record contains information about the attributes that changed during the state transition. You can get information
+about what has changed via the `changedAttributesNames()` method. This method will return an array of the attributes
+names that changed. With these attributes names, you can then use the methods `changedAttributeOldValue($attributeName)`
+and `changedAttributeNewValue($attributeName)` to get the old and new values respectively.
+
+```php
+$salesOrder = SalesOrder::create([
+    'total' => 100,
+]);
+
+$salesOrder->total = 200;
+
+$salesOrder->status()->transitionTo('approved');
+
+$salesOrder->changedAttributesNames(); // ['total']
+
+$salesOrder->changedAttributeOldValue('total'); // 100
+$salesOrder->changedAttributeNewValue('total'); // 200
+```
+
 ### Adding Validations
 
 Before transitioning to a new state, we can add validations that will allow/disallow the transition. To