fix example compilation

Author: coke

doc/Type/Capture.pod6

@@ -67,6 +67,7 @@ as named arguments and positional arguments will be passed as positional
 arguments. You may re-use the capture as many times as you want, even with
 different subroutines.
 
+=for code :preamble<my $d;my $e; sub greet {...}>
     say greet |$d;                # OUTPUT: «Mugen, 19␤»
     say greet |$e;                # OUTPUT: «Jin, 20␤»