Add PR description to changelog

changelog.md

@@ -28,6 +28,11 @@ static lifetime from a buffer that also has a static lifetime.
 * Makes the fields of the `sdl2::mixer::Channel(i32)` and `sdl::mixer::Group(i32)` structs
 public so they can be instantiated directly, and deprecates `sdl2::mixer::channel(i32)`.
 
+[PR #714](https://github.com/Rust-SDL2/rust-sdl2/pull/714)
+
+* **Breaking change** Updates the `which` fields of `sdl2::Event::ControllerDeviceAdded` and `sdl2::Event::JoyDeviceAdded` to be `u32`s so they can be used with `sdl2::GameControllerSubsystem` and `sdl::JoystickSubsystem` methods directly.
+* This should only mean removing type conversions which were previously needed to use these values, or changing incorrect assumptions in existing code.
+
 ### v0.30
 
 Re-exported sdl2\_sys as sdl2::sys