Documentation: kthread: Fix WQ_SYSFS workqueues path name

The set of WQ_SYSFS workqueues should be displayed using
"ls /sys/devices/virtual/workqueue", add the missing '/'.
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Link: https://lore.kernel.org/r/20200225124052.1506-1-yuzenghui@huawei.comSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/kernel-per-CPU-kthreads.rst

@@ -234,7 +234,7 @@ To reduce its OS jitter, do any of the following:
 	Such a workqueue can be confined to a given subset of the
 	CPUs using the ``/sys/devices/virtual/workqueue/*/cpumask`` sysfs
 	files.	The set of WQ_SYSFS workqueues can be displayed using
-	"ls sys/devices/virtual/workqueue".  That said, the workqueues
+	"ls /sys/devices/virtual/workqueue".  That said, the workqueues
 	maintainer would like to caution people against indiscriminately
 	sprinkling WQ_SYSFS across all the workqueues.	The reason for
 	caution is that it is easy to add WQ_SYSFS, but because sysfs is