Update README.md

- Install [Virtualbox](https://www.virtualbox.org/manual/ch01.html)

- Install [Vagrant](https://www.vagrantup.com/intro/getting-started/)

- Install Vagrant plugin vagrant-vbguest

- Credentials to access [ETSI forge](https://oldforge.etsi.org/!/#)

    - Set the environment variable USERNAME to your ETSI OEL account user name

    - Set the environment variable PASSWORD to your ETSI OEL account password

- Credentials to access [ETSI forge](https://forge.etsi.org/gitlab/users/sign_in)

    - Set the environment variable USERNAME to your ETSI EOL account user name

    - Set the environment variable PASSWORD to your ETSI EOL account password

Procedure:

- On your host machine, open a command line session (PuTTY, DOS window...)