workqueue: add documentation

Update copyright notice and add Documentation/workqueue.txt.

Randy Dunlap, Dave Chinner: misc fixes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-By: Florian Mickler <florian@mickler.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Dave Chinner <david@fromorbit.com>
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index f11100f..25e02c9 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -235,6 +235,10 @@
 #define work_clear_pending(work) \
 	clear_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))
 
+/*
+ * Workqueue flags and constants.  For details, please refer to
+ * Documentation/workqueue.txt.
+ */
 enum {
 	WQ_NON_REENTRANT	= 1 << 0, /* guarantee non-reentrance */
 	WQ_UNBOUND		= 1 << 1, /* not bound to any cpu */