update release notes

Author: leofang

cuda_core/docs/source/release/0.3.0-notes.rst

@@ -34,5 +34,6 @@ New examples
 Fixes and enhancements
 ----------------------
 
-- An :class:`Event` can now be used to look up its corresponding device and context using the ``.device`` and ``.context`` attributes respectively.
+- Look-up of the :attr:`Event.device` and :attr:`Event.context` (the device and CUDA context where an event was created from) is now possible.
 - The :func:`launch` function's handling of fp16 scalars was incorrect and is fixed.
+- The :class:`Device` constructor is made faster.