Download it with the "Download Now" button, then place the .modpak file in Program Files (x86)/Steam/Steamapps/common/Starbound/giraffe_storage/mods. At least, that's how you do it on Windows, may be different on Mac. If there's any more trouble, feel free to ask, I may have messed something up while uploading it to the site. And I promise I'll be faster about replying!