[PATCH] s2ram debugging documentation

Linus posted quite nice TRACE_RESUME how-to, and I think it is too nice to
be hidden in archives of mailing list, so I turned it into Documentation
piece.

Signed-off-by: Pavel Machek <pavel@suse.cz>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>