adding note about non-nullable document.domain (#2506)
adding note about non-nullable document.domain (#2506)

* adding note about non-nullable document.domain

* updating note as per dbeck comment

chrisdavidmills/browser-compat-data,mdn/browser-compat-data,chrisdavidmills/browser-compat-data,mdn/browser-compat-data,teoli2003/browser-compat-data