Add new functions to docs

Author: nickrobinson251

doc/src/base/multi-threading.md

@@ -71,3 +71,11 @@ These building blocks are used to create the regular synchronization objects.
 ```@docs
 Base.Threads.SpinLock
 ```
+
+## Task metrics (Experimental)
+
+```@docs
+Base.Experimental.task_metrics
+Base.Experimental.task_cpu_time_ns
+Base.Experimental.task_wall_time_ns
+```