Device-os Development Repository Confusion

So as mentioned in particle website, the repository for device-os firmware is in

But when I follow the README.md on ‘Getting Started’, it mentioned to clone the code from another repository (https://github.com/particle-iot/device-os/blob/develop/docs/gettingstarted.md)
git clone --recursive https://github.com/particle-iot/firmware.git

So which one is actually the right repository for the device-os? What are the difference between those two repositories?