[patch] Add description of standard_system_servicedirs into man page

[Havoc Pennington]

Hi,

Richard Hughes wrote:
> Attached patch adds a description of standard_system_servicedirs into
> the man page.
> 

Is the base directory spec relevant to the system bus, or would it be OK 
to only search the install location? A system bus looking in ~/.local or 
whatever might be wrong.

>  .TP
> +.I "<standard_system_servicedirs/>"
> +
> +.PP
> +<standard_system_servicedirs/> is equivalent to specifying a series
> +of <servicedir/> elements for each of the data directories in the "XDG
> +Base Directory Specification" with the subdirectory "dbus-1/system-services",
> +so for example "/usr/share/dbus-1/system-services" would be among the
> +directories searched.
> +
> +.PP
> +The <standard_system_servicedirs/> option is only relevant to the
> +per-system bus daemon defined in
> + at EXPANDED_SYSCONFDIR@/dbus-1/system.conf. Putting it in any other
> +configuration file would probably be nonsense.
> +