Update Period.pod6

Author: tisonkun

doc/Type/Telemetry/Period.pod6

@@ -4,9 +4,10 @@
 
 =SUBTITLE Performance data over a period
 
+    =for code :preamble<class Telemetry { }>
     class Telemetry::Period is Telemetry { }
 
-B<Note: > This class is a Rakudo-specific feature and not standard Perl 6.
+B<Note: > This class is a Rakudo-specific feature and not standard Perl 6.
 
 A C<Telemetry::Period> object contains the difference between two C<Telemetry>
 objects.  It is generally not created by calling .new, but it can be if needed:
@@ -26,6 +27,7 @@ say "Code took $period (cpu / wallclock) microseconds to execute";
 
 =head2 method perl
 
+    =for code :preamble<use Telemetry;>
     multi method perl(Telemetry::Period:D: --> Str)
 
 Returns a Perlish representation of the C<Telemetry::Period> object.