Minimal documentation of $*SAMPLER

Author: lizmat

doc/Language/variables.pod6

@@ -1175,6 +1175,10 @@ X<|$*SPEC>X<|$*TMPDIR>X<|$*THREAD>X<|$*SCHEDULER>X<|$*USAGE>
     $*SCHEDULER       | A L<ThreadPoolScheduler> object representing the current default
                       | scheduler. (see note below)
     ------------------+--------------------------------------------
+    $*SAMPLER         | The current L<Telemetry::Sampler> used for making
+                      | snapshots of system state.  Only available if
+                      | L<Telemetry> has been loaded.
+    ------------------+--------------------------------------------
 =end table
 
 Note on usage of $*SCHEDULER: