Add and test build instructions for more operating systems

[mchlmmc]

Currently README.md only covers building CirnOS on two operating systems -- Arch Linux and Fedora. It would be helpful for future developers if they could find instructions for building CirnOS for whichever operating system they may be working with.

Someone with a lot of computers running different Linux distributions or Mac OS X, Windows etc should build CirnOS on each of these devices and then provide simple instructions for how they did it on their different operating systems.

kernel.img files created on these systems should be tested and known to work before the instructions are commited to README.md.

[tilkinsc]

With the debian distro, I had luck with sudo apt-get install gcc-arm-none-eabi but I have no idea about newlib if its already integrated or not. I don't really know what it is.

For windows, I have had no luck cross compiling gcc for use with any arch. So I don't suppose you could build a arm-none-eabi gcc for linux. Some user at osdev.org or on irc told me something about you can strip with objcopy and it would work and this was with i386 or i686 archs.

Mac probably has a arm-none-eabi somewhere with a newlib since linux is similar.