workqueue: fix path to documentation

Signed-off-by: Benjamin Peterson <bp@benjamin.pe>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index a86688fa..4fa6c76 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -21,7 +21,7 @@
  * pools for workqueues which are not bound to any specific CPU - the
  * number of these backing pools is dynamic.
  *
- * Please read Documentation/workqueue.txt for details.
+ * Please read Documentation/core-api/workqueue.rst for details.
  */
 
 #include <linux/export.h>