Adds description of DESTROY to the class tutorial.
Adds description of DESTROY to the class tutorial.

This (hopefully) closes #1606

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