synergy: Update meta.description + meta.homepage.

I don't know what a "mouse keyboard" is, but instead of fixing the
description, let's use the one from the upstream README file, which is
also shorter than what we previously had.

The homepage http://synergy-foss.org/

 is outdate since ages, so let's
point to the new site.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>