Update wiki and README to reflect new way of setting up ARC2

[k00ni]

We have to update our README and wiki page(s) to outline how to get ARC2 running with 2.4+.

Fully working example should be (untested):

<?php 

$store = ARC2::getStore($arc_config);
$store->createDBCon(); // <== creates DB connection
$store->setup(); // <== checks if required tables are exist

$store->query('LOAD <http://example.org>');

Incomplete TODO list

• Adapt README
• Adapt Getting started page in the wiki: https://github.com/semsol/arc2/wiki/Getting-started-with-ARC2
• dont forget: add forgotten files to ARC2.php