introduce mkosi and Docker options

README.md

@@ -5,6 +5,22 @@ This repository, named LilyDevOS, is the replacement of
 Even if the final product will still be called LilyDev, this
 is the place where the images will be created from now on.
 
-Currently two different tools (mkosi and docker) are used,
-because mkosi containers can run only on Linux systems,
-while docker containers run everywhere.
+## mkosi or Docker images?
+
+Two different tools are used to generate the LilyDev images.
+
+**mkosi** builds a full virtual machine which can run on any OS via
+VirtualBox, libvirt or any other virtualization software. It builds
+also lightweight containers, which currently run only on Linux
+using `systemd-nspawn` (installed by default in modern distros).
+
+**Docker** was introduced later to make the lightweight LilyDev container
+available also to Windows and Mac users (but it works on Linux too!).
+
+Containers are recommended as they are lightweight and easy to use.
+Choose the image which best suits you, download the
+[latest release](releases/latest/) and follow the instuctions in
+each tool README:
+
+* [mkosi](mkosi/): recommended for Linux hosts.
+* [docker](docker/): recommended for Windows or Mac hosts.