prevent dir listings

This rule permits urls like:

    /css/
    /js/
    /img/

to show a file listing (depending on apache setup of course). By default
this most likely is not what users want
Add recommendation to use h5bp's .htaccess file

Or other server config as appropriate.
Updated minimum PHP version requirement.
Merge pull request #35 from ADmad/min-php

Updated minimum PHP version requirement.
Merge pull request #34 from FriendsOfCake/no-webroot-dir-listing

prevent dir listings