incorporate feedback from castaway++

review notes: <https://github.com/daxim/dbix-class/commit/974c7e53e3a7be75dbade6df0c4ec78cb258ca28>
* requirements/previous knowledge
* distro needs to be installed first for that code to work
* use traditional CPAN shell instead of cpanm because not everyone has it
* explain in more words what that command does
* accurate wording about connect()
* columns_info is not that useful