libpayload: Update README with Git repository URL and directory location

Change-Id: I3e068f5e6c1eb875df0885c0ce43a03082be31a5
Signed-off-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-on: http://review.coreboot.org/2228
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
1 file changed