Updated UPGRADE.md to mention JSON and Arrays support in AR

framework/UPGRADE.md

@@ -62,6 +62,10 @@ Upgrade from Yii 2.0.13
   `instanceof yii\db\Expression` in your code, you might consider changing that to checking for the interface and use the newly
   introduced methods to retrieve the expression content.
 
+* Added JSON support for PostgreSQL and MySQL as well as Arrays support for PostgreSQL on ActiveRecord layer.
+  In case you already implemented such support yourself, please switch to Yii implementation. Active Record will
+  return arrays instead of strings after data population and expects arrays to be assigned for further saving them into database.
+
 * `yii\db\PdoValue` class has been introduced to replace a special syntax that was used to declare PDO parameter type 
   when binding parameters to an SQL command, for example: `['value', \PDO::PARAM_STR]`.
   You should use `new PdoValue('value', \PDO::PARAM_STR)` instead. Old syntax will be removed in Yii 2.1.