Yii2 download page

Hi there,

I’ve realized, that on the download page (http://www.yiiframework.com/download), there is missed a one important thing - the Yii2 requirements table (see the table for Yii 1.1).

I suggest to add that list for Yii2 too in order to avoid the misunderstanding for new developers to Yii2 and keeping the consequence.