improved readme

* write description
* added cookbooks section to dependencies
use a proper license name
do not strict OS versions

This is because you couldn't actually know whenever this cookbook works
on platforms with lower versions (e.g. Ubuntu 10.04). Just for the info,
it works on Ubuntu 10.04.
Merge pull request #9 from akalyaev/update-metadata

Update metadata
Merge pull request #8 from akalyaev/improved-readme

improve readme