Update TaskScheduler docs to make it more obvious how a TaskScheduler should be put in place.

base/task_scheduler/task_traits.h

Index: base/task_scheduler/task_traits.h
diff --git a/base/task_scheduler/task_traits.h b/base/task_scheduler/task_traits.h
index c2e372829447996bcf80c01261cab4dc5f377f38..435fdac9af3843d18cec36bd441dacb6e74f91cf 100644
--- a/base/task_scheduler/task_traits.h
+++ b/base/task_scheduler/task_traits.h
@@ -127,7 +127,7 @@ class BASE_EXPORT TaskTraits {
   // removing usage of methods listed above in the labeled tasks would still
   // result in tasks that may block (per MayBlock()'s definition).
   //
-  // In doubt, consult with base/task_scheduler/OWNERS.
+  // In doubt, consult with //base/task_scheduler/OWNERS.
   TaskTraits& WithBaseSyncPrimitives();
 
   // Applies |priority| to tasks with these traits.