README: Updated current Vagrant & VirtualBox versions.

Author: ramiro

README.md

@@ -21,12 +21,12 @@ Preparation
 ### Software installation
 
 First of all, you need to install the latest versions of
-[Vagrant 1.9.1](https://www.vagrantup.com/downloads.html) and
-[VirtualBox 5.1.14](https://www.virtualbox.org/wiki/Downloads) on your host
-machine.
+[Vagrant](https://www.vagrantup.com/downloads.html) (at version 2.0.1 as of
+now) and [VirtualBox](https://www.virtualbox.org/wiki/Downloads) (currently at
+version 5.2.4) on your host machine.
 
-If you use a version of VirtualBox that isn't 5.1.6 you may run into problems
-creating the NFS mount. You can either upgrade to VirtualBox 5.1.6, or you can
+If you use a version of VirtualBox that isn't 5.1.6 or newer you may run into
+problems creating the NFS mount. You can either upgrade VirtualBox, or you can
 try to install the [vagrant-vbguest](https://github.com/dotless-de/vagrant-vbguest)
 plugin, which will attempt to install your local version of GuestAdditions into
 the VM.