nixos: added installation doc for nspawn container

nixos/doc/manual/installation/installing-nspawn-container.xml

@@ -0,0 +1,37 @@
+<section xmlns="http://docbook.org/ns/docbook"
+         version="5.0"
+         xml:id="sec-installing-nspawn-container">
+ <title>Installing into a nspawn container</title>
+
+ <para>
+  For installing a NixOS into a systemd nspawn container the NixOS installation tools are needed.
+  If you run another distribution than NixOS on your host,
+  please follow <xref linkend="sec-installing-from-other-distro"/> steps 1, 2, and 3.
+ </para>
+
+ <para>
+  Create a NixOS configuration file <filename>/var/lib/machines/my-container/etc/nixos/configuration.nix</filename>.
+  It is important that the container root file system is under <filename>/var/lib/machines</filename>.
+  This is the standard location where <command>machinectl</command> will look for containers.
+  If you choose place the root into another location you need to start the container directly with <command>systemd-nspawn</command>.
+  The file needs to have at least following options enabled:
+<programlisting>
+<xref linkend="opt-boot.isContainer"/> = true;
+<xref linkend="opt-boot.loader.initScript.enable"/> = true;
+</programlisting>
+  If your host uses <command>systemd-networkd</command> to configure the network,
+  you can also enable <xref linkend="opt-networking.useNetworkd"/> to use networkd default network configuration for your host and container.
+ </para>
+
+ <para>
+  Install the container by running following command:
+   <screen>nixos-install --root /var/lib/machines/my-container \
+     --no-channel-copy --no-root-passwd --no-bootloader</screen>
+ </para>
+
+ <para>
+  Start the container by running following command:
+  <screen>machinectl start my-container</screen>
+ </para>
+
+</section>

nixos/doc/manual/installation/installing.xml

@@ -563,5 +563,8 @@ Retype new UNIX password: ***</screen>
   <xi:include href="installing-from-other-distro.xml" />
 
   <xi:include href="installing-behind-a-proxy.xml" />
+
+  <xi:include href="installing-nspawn-container.xml" />
+
  </section>
 </chapter>