Add Dockerfile build section to readme

Signed-off-by: Ruben Jenster <[email protected]>

README.md

@@ -11,10 +11,23 @@ a drop-in container runtime replacement for use by [CRI-O](https://github.com/ku
 With liblxc starting from [lxc-4.0.0-927-gb5daeddc5](https://github.com/lxc/lxc/commit/b5daeddc5afce1cad4915aef3e71fdfe0f428709)
 it passes all sonobuoy conformance tests.
 
-## Installation
+## Build
 
-For the installation of the runtime see [install.md](doc/install.md)</br>
-For the installation and initialization of a kubernetes cluster see [kubernetes.md](doc/kubernetes.md)
+You can use the provided [Dockerfile](Dockerfile) to build an</br>
+
+runtime only image (`lxcri` + `lxc`)
+
+`docker build --build-arg installcmd=install_runtime`
+
+or with everything required for a kubernetes node (kubelet, kubeadm, cri-o, lxcri, lxc ...)
+
+`docker build`
+
+Note: The images are not pre-configured and you must follow the steps in setup for now.
+
+## Setup
+
+To use `lxcri` as OCI runtime in `cri-o` see [install.md](doc/install.md)
 
 ## API Usage