Mention representation of closure-captured vars.
Mention representation of closure-captured vars.

Thanks @non for the suggestion and link.

typelevel/typelevel.github.com,S11001001/typelevel.github.com,typelevel/typelevel.github.com,melrief/typelevel.github.com,melrief/typelevel.github.com,S11001001/typelevel.github.com,melrief/typelevel.github.com,S11001001/typelevel.github.com,melrief/typelevel.github.com,S11001001/typelevel.github.com,typelevel/typelevel.github.com