README: Add PuppetDB 3 requirement
README: Add PuppetDB 3 requirement
stoyansbg/puppetboard,mterzo/puppetboard,mterzo/puppetboard,mterzo/puppetboard,james-powis/puppetboard,tparkercbn/puppetboard,holstvoogd/puppetboard,voxpupuli/puppetboard,grandich/puppetboard,johnzimm/xx-puppetboard,johnzimm/xx-puppetboard,puppet-community/puppetboard,johnzimm/puppetboard,holstvoogd/puppetboard,puppet-community/puppetboard,mterzo/puppetboard,voxpupuli/puppetboard,grandich/puppetboard,stoyansbg/puppetboard,tjayl/puppetboard,johnzimm/puppetboard,stoyansbg/puppetboard,johnzimm/xx-puppetboard,puppet-community/puppetboard,james-powis/puppetboard,tjayl/puppetboard,james-powis/puppetboard,grandich/puppetboard,holstvoogd/puppetboard,johnzimm/puppetboard,tjayl/puppetboard,tparkercbn/puppetboard,tparkercbn/puppetboard,grandich/puppetboard,tparkercbn/puppetboard,voxpupuli/puppetboard,johnzimm/xx-puppetboard