Added --prefer-dist to all docs
Added --prefer-dist to all docs

1. It results in much smaller download and takes less disk space (25MB instead of 180MB for yii-basic + dependencies).
2. It requires less utilities to be installed (no VCS binaries required).
3. It takes less time to install dependencies.

U-D13/yii2-twig,U-D13/yii2-twig