How to build Magento developer documentation locally

Sometime, it is slow to access Magneto official developer documents, luckily, Magneto provide fully document in its Github,  we can download it and build on our local Ubuntu OS, the details is as follows. In order to build the documentation, we need ruby 2.0 up, check if you OS already has ruby installed: [crayon-5c440e1e6b85d653656205/] if [...]