man,units: fix installation of systemd-nspawn@.service and add example

TODO

@@ -504,6 +504,7 @@ Features:
   - nspawn: maybe add a way to drop additional caps, in addition to add additional caps
   - nspawn: maybe explicitly reset loginuid?
   - nspawn: make it work for dwalsh and shared /usr containers -- tmpfs mounts as command line parameters, selinux exec context
+  - refuses to boot containers without /etc/machine-id (OK?), and with empty /etc/machine-id (not OK).
 
 * cryptsetup:
   - cryptsetup-generator: allow specification of passwords in crypttab itself

man/systemd-nspawn.xml

@@ -409,6 +409,18 @@
                 boots an OS in a namespace container in it.</para>
         </refsect1>
 
+        <refsect1>
+                <title>Example 4</title>
+
+                <programlisting># mv ~/arch-tree /var/lib/container/arch
+# systemctl enable systemd-nspawn@arch.service
+# systemctl start systemd-nspawn@arch.service</programlisting>
+
+                <para>This makes the Arch Linux container part of the
+                <filename>multi-user.target</filename> on the host.
+                </para>
+        </refsect1>
+
         <refsect1>
                 <title>Exit status</title>
 

units/systemd-nspawn@.service.in

@@ -14,4 +14,4 @@ ExecStart=@bindir@/systemd-nspawn -bjD /var/lib/container/%i
 Type=notify
 
 [Install]
-Also=multi-user.target
+WantedBy=multi-user.target