Bug#789652: installation-guide: improve explanations about rebooting, etc

[Vincent McIntyre <vincent.mcintyre@csiro.au>]

Package: installation-guide
Tags: patch

thanks

see also #760923.

Not sure this is quite correct for powerpc.

Index: manual/en/post-install/shutdown.xml
===================================================================
--- manual/en/post-install/shutdown.xml	(revision 69984)
+++ manual/en/post-install/shutdown.xml	(working copy)
@@ -21,11 +21,23 @@
 <keycap>Ctrl</keycap> <keycap>Alt</keycap> <keycap>Del</keycap> </keycombo>
 <phrase arch="powerpc"> or <keycombo> <keycap>Control</keycap>
 <keycap>Shift</keycap> <keycap>Power</keycap> </keycombo> on Macintosh
-systems</phrase>. A last option is to log in as root and type one of the
-commands <command>poweroff</command>, <command>halt</command> or
-<command>shutdown -h now</command> if either of the key combinations do not
-work or you prefer to type commands; use <command>reboot</command> to reboot
-the system.
+systems</phrase> to reboot the system.
+If the key combinations do not work, a last option is to log in as root
+and type the necessary commands.
+Use <command>reboot</command> to reboot the system.
+Use <command>halt</command> to halt the system without powering it off
+footnote>
 
+<para>
+This behaviour was introduced in the jessie release, by the systemd init system.
 </para>
+
+</footnote>.
+To power off the machine, use <command>poweroff</command> or
+<command>shutdown -h now</command>.
+Note that the <package>systemd-sysv</package> package replaces these
+commands with calls to the <command>systemctl</command> command; for example
+<command>systemctl reboot</command> for rebooting.
+
+</para>
  </sect1>