Whenever there is an update for Divinity on Steam, and assuming your library is in detailed mode (where you see a list of games and information (achievements, news, etc) on the selected title), just select Divinity from the list and look under the achievement section. There's a "Recent News" section and the update notes are placed there.
Sometimes it takes a few minutes for them to show up once the patch has been released. Larian has been pretty quick at getting them up there, though.
