README: Consolidate discussions of -stable patches

The nature of the patches for the -stable kernels was discussed
twice; this commit consolidates those discussions into one
paragraph.

Signed-off-by: Michael Witten <mfwitten@gmail.com>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>