This change borrowed from Terraform's [archived provider
documentation](https://www.terraform.io/docs/internals/archiving.html)
adds a documentation partial that can be applied to any provisioner
plugin that is not actively maintained by Packer or the community. A
call to action for anyone interested in supporting the plugin has been
added to the Packer README until a better location is made available.
* Mark the salt-masterless plugin as unmaintained
652d2a4e9e