Add release note for Device.arch property

Co-authored-by: leofang <5534781+leofang@users.noreply.github.com>

Author: Copilot

cuda_core/docs/source/release/0.X.Y-notes.rst

@@ -24,7 +24,7 @@ Breaking Changes
 New features
 ------------
 
-None.
+- Added :attr:`Device.arch` property that returns the compute capability as a string (e.g., '75' for CC 7.5), providing a convenient alternative to manually concatenating the compute capability tuple.
 
 
 New examples