Clarify topic variable's status in for loop
Clarify topic variable's status in for loop

Issue: https://github.com/perl6/doc/issues/3075

MasterDuke17/doc,tbrowder/doc,MasterDuke17/doc,perl6/doc,MasterDuke17/doc,MasterDuke17/doc,tbrowder/doc,tbrowder/doc,perl6/doc,perl6/doc,tbrowder/doc,perl6/doc,perl6/doc