So you want to hack on the kernel
It seems that Greg KH had gotten fed up with people (SGI, more SGI, IBM, OSDL Japan) trying to get their patches into the Linux kernel without understanding how the kernel is being developed or maintained. So he has decided to write a HOWTO for beginning kernel developers. He wants to eventually see the document in the kernel source itself (either in the root or in Documentation), but meanwhile you can view the latest revision here in his git repositiory.
Very enlightening reading for anyone who wants to understand, or contribute to, kernel development. IMHO, this HOWTO should be in the kernel source root — I know that the first time I looked at the kernel source, I had absolutely no idea where to start, and 90% of the stuff in Documentation was relevant only to obsolete hardware that I did not have.