Add changelog for release 0.4

Author: sosthene-nitrokey

CHANGELOG.md

@@ -0,0 +1,15 @@
+# Changelog
+
+## Unreleased
+
+## [v0.4.0][] (2024-06-20)
+
+- Update `heapless` to version `0.8` ([#3][])
+- Remove the `Deref` implementation to `heapless` and implement `Deref<Target = [u8]>` directly ([#8][])
+- Add conversions between `[u8; N]` and `heapless::Vec<u8, N>`. The `heapless` conversions are behind the `heapless-0.8` feature flag so that `heapless` can be bumped without a semver-breaking change in the future ([#6][] and [#8][])
+
+[#3]: https://github.com/trussed-dev/heapless-bytes/pull/3
+[#6]: https://github.com/trussed-dev/heapless-bytes/pull/6
+[#8]: https://github.com/trussed-dev/heapless-bytes/pull/8
+
+