You should be able to do it by copying the
synergy.desktop file into your
~/.config/autostart/ folder by running the following command:
cp /usr/share/applications/synergy.desktop ~/.config/autostart/
then all you should have to do is to set the permissions on the file:
chmod 664 ~/.config/autostart/synergy.desktop
EDIT: I know this was written a while ago, but you can also just copy the file to the xdg/autostart so that it starts before logging in, probably best to not copy it into both locations so it doesn't start more than once:
sudo cp /usr/share/applications/synergy.desktop /etc/xdg/autostart/
sudo chmod 644 /etc/xdg/autostart/synergy.desktop
Now when you reboot your host it should autostart synergy.
Hope this helps!