Add a script for extracting a part of the built docker image

extract-docker.sh

@@ -0,0 +1,12 @@
+#!/bin/sh
+
+if [ $# -lt 2 ]; then
+    echo $0 image dir
+    exit 1
+fi
+
+image=$1
+dir=$2
+
+rm -rf $dir
+docker run --rm $image tar -cf - $dir | tar -xvf -