mention take-rw

Author: gfldex

doc/Language/control.pod6

@@ -404,6 +404,8 @@ from within C<gather>:
 
     say weird(<a b c>, :direction<backward> );          # (c b a)
 
+If values need to be mutable on the caller side, use L<take-rw|/type/Mu#routine_take-rw>.
+
 
 =head1 X<given|control flow>
 X<|switch (given)>