Add CHANGELOG entry

CHANGELOG.md

@@ -46,6 +46,12 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 - Errno aliases are now associated consts on `Errno`, instead of consts in the
   `errno` module.
   (#[1452](https://github.com/nix-rust/nix/pull/1452))
+- Nix's error type is now a simple wrapper around the platform's Errno.  This
+  means it is now `Into<std::io::Error>`.  It's also `Clone`, `Copy`, `Eq`, and
+  has a small fixed size.  It also requires less typing.  For example, the old
+  enum variant `nix::Error::Sys(nix::errno::Errno::EINVAL)` is now simply
+  `nix::Error::EINVAL`.
+  ([#1446](https://github.com/nix-rust/nix/pull/1446))
 
 ### Fixed
 - Allow `sockaddr_ll` size, as reported by the Linux kernel, to be smaller then it's definition