DOCS-10621 add Belongs To section to tutorial, including :optional option description
DOCS-10621 add Belongs To section to tutorial, including :optional option description

kay-kim/mongoid,kay-kim/mongoid,herimedia/mongoid,jonhyman/mongoid,mongodb/mongoid,Welovroi/mongoid,mongodb/mongoid,jonhyman/mongoid,Welovroi/mongoid,herimedia/mongoid,mongodb/mongoid