Add xz-utils dependency

Closes #90

Dockerfile

@@ -4,7 +4,7 @@ RUN apt-get -y update && \
     apt-get -y install \
         git vim parted \
         quilt realpath qemu-user-static debootstrap zerofree pxz zip dosfstools \
-        bsdtar libcap2-bin rsync grep udev \
+        bsdtar libcap2-bin rsync grep udev xz-utils \
     && rm -rf /var/lib/apt/lists/*
 
 COPY . /pi-gen/

README.md

@@ -13,7 +13,7 @@ On Debian-based systems:
 
 ```bash
 apt-get install quilt parted realpath qemu-user-static debootstrap zerofree pxz zip \
-dosfstools bsdtar libcap2-bin grep rsync
+dosfstools bsdtar libcap2-bin grep rsync xz-utils
 ```
 
 The file `depends` contains a list of tools needed.  The format of this

depends

@@ -10,3 +10,4 @@ capsh:libcap2-bin
 bsdtar
 grep
 rsync
+xz:xz-utils