fixed note about post redirect get

Fixed guide example by adding note about redirect / refresh . See this [comments](https://github.com/yiisoft/yii2/commit/0e18fbf89331305d5caed7ae5aafe176154bc1d3#commitcomment-6620020) for more info .
ok, what about russian guide ? I need to revert changes and then follow this [guide](https://github.com/yiisoft/yii2/blob/master/docs/internals-ru/translations.md) .