Fix incorrect reference to `rentalUnit` variable.
Fix incorrect reference to `rentalUnit` variable.

This paragraph references a `rentalUnit` variable that's passed into the component, but the correct name of the variable is `rental`. This updates the paragraph to match the code.

A clearer option could be to leave the paragraph as-is, and *actually* name the variable `rentalUnit` in the code here and in `model-hook.md`.

nicobot/guides,MarkMT/guides,MarkMT/guides,bmac/guides,davidpett/guides,knownasilya/guides,skaterdav85/guides,bmac/guides,bmac/guides,knownasilya/guides,skaterdav85/guides,tleskin/guides,jkarsrud/guides,ubuntuvim/guides,HeroicEric/guides,davidpett/guides,jkarsrud/guides,HeroicEric/guides,knownasilya/guides,MarkMT/guides,jkarsrud/guides,davidpett/guides,skaterdav85/guides,ubuntuvim/guides,skaterdav85/guides,ubuntuvim/guides,MarkMT/guides,HeroicEric/guides,nicobot/guides,tleskin/guides,bmac/guides,tleskin/guides,ubuntuvim/guides,jkarsrud/guides,nicobot/guides,davidpett/guides,knownasilya/guides