Update contrib/vagrant-docker with projects available

contrib/vagrant-docker/README.md

@@ -1,3 +1,19 @@
-# Vagrant-docker
+# Vagrant integration
 
-This is a placeholder for the official vagrant-docker, a plugin for Vagrant (http://vagrantup.com) which exposes Docker as a provider.
+Currently there are at least 4 different projects that we are aware of that deals
+with integration with [Vagrant](http://vagrantup.com/) at different levels. One
+approach is to use Docker as a [provisioner](http://docs.vagrantup.com/v2/provisioning/index.html)
+which means you can create containers and pull base images on VMs using Docker's
+CLI and the other is to use Docker as a [provider](http://docs.vagrantup.com/v2/providers/index.html),
+meaning you can use Vagrant to control Docker containers.
+
+
+### Provisioners
+
+* [Vocker](https://github.com/fgrehm/vocker)
+* [Ventriloquist](https://github.com/fgrehm/ventriloquist)
+
+### Providers
+
+* [docker-provider](https://github.com/fgrehm/docker-provider)
+* [vagrant-shell](https://github.com/destructuring/vagrant-shell)