[PATCH] update Doc/oops-tracing.txt for TAINT_USER

Add TAINT_USER description to Tainted flags in oops-tracing.txt.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>