Resolve name conflit in volt templates between 'tag' variable and 'Phalcon\Tag'; Added coment to Index.php

There was a conflict in volt templates for the variable 'tag' and the 'Phalcon\Tag' names. I changed the variable in volt templates from 'tag' to 'tagItem' to prevent this errors;

I also added a comment to the index.php file for users to setup the project in the document_root folder to setup correctly the setBaseUri parameter.