Add napari instruction to readme

README.md

 # VM ansible playbooks
 
-A collection of Ansible playbook to install software on GRADES virtual machines
\ No newline at end of file
+A collection of [Ansible playbook](https://docs.ansible.com/ansible/latest/user_guide/playbooks.html) to install software on GRADES Virtual Machines (VM). 
+
+These playbooks allow to run receipies to install stuff after the creation of the VM via:
+https://docs.ansible.com/ansible/latest/user_guide/playbooks.html
+
+## First Install Ansible
+
+Open a terminal an type:
+
+```bash
+export PATH=$PATH:/home/guest/.local/bin && python3 -m pip install ansible 
+```
+
+## Run ansible with a given playbook name
+
+Playbook are loaded directly from this git repo thanks to ansible-pull command. 
+
+### Install Napari
+
+```bash
+ansible-pull -U https://gitlab.com/soleil-data-treatment/soleil-beamlines/soleil-beamline-disco/vm-ansible-playbooks.git napari.yml
+```
+
+After some time you will see an icon Napari on the desktop, just double click on it to launch Napari.