Add note about unsupported repo

[briancain]

Hey there @mitchellh - We were hoping that we could get a note on this repo to let people know that this plugin is no longer supported. I think maybe @rtyler is a maintainer too? Either way, it doesn't look like there's been much traction on any of the issues or pull requests, so it would be nice to let folks know that this plugin isn't really being supported. There has been some confusion around if this is something official (since it's on @mitchellh 's page) and supported, since there are other HashiCorp tools where this is true.

The other alternative is the archive this repo so it's clear that support has stopped. That would prevent others from contributing fixes or opening issues, but it doesn't look like those are being triaged anyway. At the very least, this pull request adds a note to the README and new issue templates to let folks know what's going on.

Hope that makes some sense! Let me know if there's anything I can do, thanks!

[boldandbusted]

Sadly, this is even made more glaring as the Vagrant Plugin development documentation uses this repo as an example for others to follow. Ref: https://www.vagrantup.com/docs/plugins/packaging :(

[igorlg]

+1 to this PR. As an alternative, finding a new maintainer would also be great. Since this is such a popular Plug-in, I doubt it would be difficult to find someone.

And yes, I'm putting my hand up for it if @mitchellh is interested :)