Add redhat to supported platforms in readme.
Add redhat to supported platforms in readme.

archii/puppet-collectd,voxpupuli/puppet-collectd,archii/puppet-collectd,voxpupuli/puppet-collectd,voxpupuli/puppet-collectd,juniorsysadmin/puppet-collectd,archii/puppet-collectd,juniorsysadmin/puppet-collectd