kern-tools: symbol-why fix and README update

There was a bad indent in symbol_why, which we fix with a submitted
patch. As part of getting that patch, it was pointed out that there's
no README telling people where to send changes. So we add a basic
README to avoid that in the future:

   8f6aaab docs: add README for patch submission
   9f1a6cb symbol_why: fix incorrect indentation of sys.exit(1)

Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>