If you don't know where to look it can take a surprisingly long time to find things like: https://github.com/torvalds/linux/blob/master/Documentation/.... It is obvious once you know, but unless you know are in the habit of checking all the 'likely places' such a doc would be you are going to be lost. While one could allow annotations on top of files in github it would completely fragment real and important documentation efforts and leave information scattered in 10 different locations that no one could pull back together.