diff --git a/tools/osbuilder/README.md b/tools/osbuilder/README.md
index 783a535a40..9ea99e8518 100644
--- a/tools/osbuilder/README.md
+++ b/tools/osbuilder/README.md
@@ -95,6 +95,9 @@ filesystem components to generate an initrd.
 3. When generating an image, the initrd is extracted to obtain the base rootfs for
 the image.
 
+CentOS is the default distro for building the rootfs, to use a different one, you can set `DISTRO=<your_distro>`.
+For example `make USE_DOCKER=true DISTRO=ubuntu rootfs` will make Ubuntu rootfs using Docker.
+
 ### Rootfs creation
 
 This section shows how to build a basic rootfs using the default distribution.