Add vbox drivers

docs/ubuntu-persistent-installation.md

@@ -40,3 +40,11 @@ sudo apt-get -y install curl
 export PERSISTENT=
 bash <(curl -sSL raw.githubusercontent.com/01-edu/public/master/scripts/kickstart.sh)
 ```
+
+After reboot you should install Virtual Box additions (and reboot again) :
+
+```shell
+apt -y install virtualbox-guest-x11
+```
+
+Then it is advised to use the virtual machine in full screen mode (Host key - F)