push/pull: adjust missing upstream help text to changed interface

push/pull: adjust missing upstream help text to changed interface

In case of a missing upstream, the git-parse-remote script suggests:

If you wish to set tracking information for this branch you can do so
with:

    git branch --set-upstream nsiv2 origin/<branch>

But --set-upstream is deprectated. Change the suggestion to:

    git branch --set-upstream-to=origin/<branch> nsiv2

Reported-by: Jeroen van der Ham <vdham@uva.nl>
Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Jeff King <peff@peff.net>