Fixed #23224 - Document EmailValidator domain whitelist parameter

"email domains" (plural)

Would be helpful to explain the logic here (regular expressions are used to validate domains that don't appear in the whitelist) as well as the use case of adding a domain without a top-level domain since those don't pass the regex test.

Could you also add a link to this class from models.EmailField. Something like, "Uses EmailValidator to validate the input."