Added info how to setup puppet-dlrn on puppet 6
Added info how to setup puppet-dlrn on puppet 6

Current README file doesn't provide how to install
puppet-dlrn on new puppet release.

Change-Id: I7387aac8658eabd08b0b7ea3774407cf298f6d80

rdo-infra/puppet-dlrn,rdo-infra/puppet-dlrn,javierpena/puppet-delorean,javierpena/puppet-delorean,rdo-infra/puppet-dlrn,javierpena/puppet-delorean