Kernel documentation

[Lisi <lisi.reisz@gmail.com>]

<quote>
We advise studying the README files in this root directory of the kernel 
source, and Documentation/Changes or the documentation index of the kernel in 
Documentation/00-INDEX.
</quote>

Presumably I have to download a kernel source to get at the README, but where 
can I find the Documentation/00-INDEX?

If I download an older kernel than the one that I am using, in oredr to read 
the README file,  will GRUB continue to use the present newer kernel?  I am 
still not very confident about editing GRUB 2.

And yes, I have googled - and I'm afraid that I found the answers as clear as 
mud. :-(

Thanks,
Lisi