bin/51243: Add valid examples to pcictl(8)

[coypu%sdf.org@localhost]

>Number:         51243
>Category:       bin
>Synopsis:       Add valid examples to pcictl(8)
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    bin-bug-people
>State:          open
>Class:          doc-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Jun 15 03:40:00 +0000 2016
>Originator:     coypu
>Release:        NetBSD-7.99.30
>Organization:
>Environment:
NetBSD  7.99.30 NetBSD 7.99.30 (GENERIC) #3: Fri Jun 10 15:20:40 IDT 2016  fly%net.Home@localhost:/usr/obj/sys/arch/amd64/compile/GENERIC amd64
>Description:
Maybe in retrospect the syntax is legible, reading:
SYNOPSIS
  pcictl pcibus command [arg [...]]

then
  the following commands are available:

  list [-Nn] [-b bus] [-d device] [-f function]

  any-other-command [-b bus] -d device ...

does not make me try "pcictl pci0 list" as the first try (or first 10 tries, my attempts were all "pcictl list -d pci0" and variants)

an example or two will be nice.
writing then man page as pcibus list ... is also nice.

nicer still, make pcictl list work without any argument, listing for all pci buses.
>How-To-Repeat:

>Fix: