Improve the README

Add requirements, how to guide, etc.

README.md

@@ -1,5 +1,41 @@
 # Libvirt-friendly definitions for common operating systems
 
-Libvirt, the most common virtualization library on Linux, uses XML to store definitions of virtual machines. 
+Libvirt, the most common virtualization library on Linux, uses XML to store the definition of a virtual machine.
 
-This repository's goal is to maintain definitions that are optimized for running common operating systems.
+[The reference Domain XML format webpage](https://libvirt.org/formatdomain.html), which lists most of the accepted parameters that can be used to define a virtual machine, is almost 100 pages long. It is daunting to pick the most optimized parameters for running a particular guest operating system (OS) well.
+
+This repository's goal is to maintain definitions that are tuned for running modern OS, leveraging as many paravirtualized devices (virtio) the target guest OS support.
+
+## Requirements
+
+It is expected that libvirt and other dependencies such as QEMU are already installed and that such tools are already correctly configured.
+
+* At least QEMU emulator version 7.0.0
+* At least libvirt 8.6.0
+
+## How to use it
+
+* Clone this repository locally
+
+### Session-driven virtual machines
+
+* Navigate to the session directory
+* Choose your target OS of choice and, as a normal user, use the following `virsh` command to define a virtual machine:
+
+```
+$ virsh define linux.xml 
+```
+
+### System-driven virtual machines
+
+* Navigate to the system directory
+* Choose your target OS of choice and, as a root user, use the following `virsh` command to define a virtual machine:
+
+```
+# virsh define linux.xml
+```
+
+## Ressources
+
+* Domain XML format for libvirt: https://libvirt.org/formatdomain.html
+* qemu:///system vs qemu:///session, a great article by Cole Robinson: https://blog.wikichoon.com/2016/01/qemusystem-vs-qemusession.html