cd ~/Library/Application\ Support/Coda\ 2
git clone --recursive git@github.com:zenangst/Coda-2-Modes.git Modes
cd ~/Library/Containers/com.panic.Coda2/Data/Library/Application\ Support/Coda\ 2
git clone --recursive git@github.com:zenangst/Coda-2-Modes.git Modes
Remember that if you have a Modes directory you should move that aside in order to use this new one.
If you want to get the latest updates, you simply run git pull inside the Modes directory
cd ~/Library/Application\ Support/Coda\ 2
git pull --recurse-submodules
Or the following if you are running the sandboxed MAS version.
cd ~/Library/Containers/com.panic.Coda2/Data/Library/Application\ Support/Coda\ 2
git pull --recurse-submodules