This is a small update for the structure of the docs about building Ray from source.
My idea was to isolate steps that are shared and then steps required per platform/system. Also consolidating the instructions to clone with git, install, directory structure, etc.
I'm still figuring out the building steps (installing the dependencies for docs in an M1), but I wanted to start the draft right away.
In the [docs contributing page](https://docs.ray.io/en/master/ray-contribute/docs.html), the links to other docs pages point to master/ instead of latest/, which can be a bit confusing since this is not the live version of the docs that people will be used to seeing.
I added a couple additional clarifications and fixed a typo as well. I also mentioned the need for an image and linked to the image directory (though some subprojects have their own image directories as well, which I did not mention).
