specfile: PREFIX is %{_prefix} instead of "/usr"

i might want to build an rpm for FreeBSD you know. /jk
while i'm not aware of any rpm-using OS with a different value,
this bit of flexibility does not hurt.
specfile: make all runs in the %build script

where it belongs.
manpage: typo
README.rest: markup changes

docutils' option list renders optargs using slanted
fixed-width font; it appears italics and fixed-width
cannot be combined using inline markup; so far i opted
to have them rendered with straight fixed-width.
this was prone to confusion re what is a placeholder
vs. an actual literal, so i'm going for italics instead.
docs have two examples

the pre-existing one comes with more prose, its config file
is produced with cat(1) (looks less pretentious than the earlier
printf(1)-based stuff, even though it's not as copy-pastable)

the new example needs some love.