Update changelog for 0.4.0

Author: diptorupd

CHANGELOG.md

@@ -2,6 +2,8 @@
 All notable changes to this project will be documented in this file.
 
 ## [Unreleased]
+
+## [0.4.0] - 2020-11-04
 ### Added
 - Device descriptors "max_compute_units", "max_work_item_dimensions", "max_work_item_sizes", "max_work_group_size", "max_num_sub_groups" and "aspects" for int64 atomics inside dpctl C API and inside the dpctl.SyclDevice class.
 - MemoryUSM* classes moved to `dpctl.memory` module, added support for aligned allocation, added support for `prefetch` and `mem_advise` (sychronous) methods, implemented `copy_to_host`, `copy_from_host` and `copy_from_device` methods, pickling support, and zero-copy interoperability with Python objects which implement `__sycl_usm_array_inerface__` protocol.