Update index.markdown
Update index.markdown

Document postgres 9.4 dependency in system requirements.
senior/puppetdb,mullr/puppetdb,senior/puppetdb,kbarber/puppetdb,senior/puppetdb,waynr/puppetdb,mullr/puppetdb,kbarber/puppetdb,kbarber/puppetdb,mullr/puppetdb,rbrw/puppetdb,rbrw/puppetdb,waynr/puppetdb,kbarber/puppetdb,puppetlabs/puppetdb,puppetlabs/puppetdb,rbrw/puppetdb,rbrw/puppetdb,rbrw/puppetdb,mullr/puppetdb,senior/puppetdb,waynr/puppetdb,puppetlabs/puppetdb,waynr/puppetdb,puppetlabs/puppetdb,mullr/puppetdb,puppetlabs/puppetdb