Assuming Ronin is downloaded and extracted to ~/Downloads/ronin-main
See https://github.com/MacGapProject/MacGap1 for details

sudo gem install macgap
mkdir ~/tmp
cd ~/tmp
macgap new Ronin
cp ~/Downloads/ronin-main/index.html Ronin/
macgap build Ronin
open ./Ronin.app

thanks.  worked great with Ronin.  

The menu bar seems upside down, any known fixes?