Correct Linux staff client build instructions

Correct Linux staff client build instructions

There were a few things going on here; 2.3 introduced linux32-client and
linux64-client targets, so the old linux-client Make target no longer
worked.

Also, Wine isn't generally how many of us would recommend running staff
clients when there's a perfectly good native client likely to better
support printing, etc.

Also, rather than pointing at evergreen-ils.org for downloads, which
won't work in many situations (and which prevents the use of the
auto-update mechanism), use the "updates" target to point at the locally
downloadable clients. Eventually we'll properly document the use of
auto-updates, but for now this is hopefully a step in the right
direction.

Signed-off-by: Dan Scott <dscott@laurentian.ca>
Signed-off-by: Ben Shum <bshum@biblio.org>