emphasize VMM is linux only for now

Author: leofang

cuda_core/docs/source/release/0.4.0-notes.rst

@@ -33,7 +33,7 @@ New features
 - Stream-ordered memory allocation can now be shared on Linux via :class:`DeviceMemoryResource`.
 - Added NVVM IR support to :class:`Program`. NVVM IR is now understood with ``code_type="nvvm"``.
 - Added an :attr:`ObjectCode.code_type` attribute for querying the code type.
-- Added :class:`VirtualMemoryResource` for low-level virtual memory management.
+- Added :class:`VirtualMemoryResource` for low-level virtual memory management on Linux.
 
 
 New examples