Add explicit steps for installing vagrant on Debian / Ubuntu

Readme.md

@@ -17,7 +17,13 @@ If your software mentions all build dependencies in its SPEC file, you don't nee
 
 ## Vagrant Installation
 
-Previously you could install vagrant via rubygems (e.g. using bundler), but since 1.1.x this method is deprecated, so please go to http://downloads.vagrantup.com/ and download the latest package for your operating system
+Previously you could install vagrant via rubygems (e.g. using bundler), but since 1.1.x this method is deprecated, so please go to http://downloads.vagrantup.com/ and download the latest package for your operating system. On Debian / Ubuntu run the f.ex. following command.
+
+```bash
+gem uninstall vagrant
+wget http://files.vagrantup.com/packages/87613ec9392d4660ffcb1d5755307136c06af08c/vagrant_x86_64.deb
+sudo dpkg -i vagrant_x86_64.deb
+```
 
 Install a vagrant plugin to keep the virtualbox guest additions up-to-date.