README.md: Clarify hiera use and provide better examples
README.md: Clarify hiera use and provide better examples

This addresses the issues from #41.

netors/puppet-php,cgalvarez/puppet-php,glorpen/puppet-php,mmoll/puppet-php,NickelMedia/puppet-php,mayflower/puppet-php,netors/puppet-php,glorpen/puppet-php,mayflower/puppet-php,NickelMedia/puppet-php,cgalvarez/puppet-php,mmoll/puppet-php