Update README links to reflect changes in referenced repository
Update README links to reflect changes in referenced repository

The current links 404 following a reorganisation of the
`alphagov/packager` repository and the tooling used to create
Ubuntu packages used.  Update the links so they direct somewhere
useful.

gds-operations/puppet-unattended_reboot,gds-operations/puppet-unattended_reboot,gds-operations/puppet-unattended_reboot