Add changelog entries

Author: thendiscard

CHANGELOG.md

@@ -16,7 +16,13 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Changed
 ### Fixed
+
 ### Removed
+- Removed `lutimes` on OpenBSD as it is not implemented on OpenBSD.
+  ([#1000](https://github.com/nix-rust/nix/pull/1000))
+- Removed `fexecve` on NetBSD and OpenBSD. Although rust-lang/libc includes it
+  (under `unix/bsd/netbsdlike/`) `fexecve` is not currently implemented on NetBSD
+  nor on OpenBSD. ([#1000](https://github.com/nix-rust/nix/pull/1000))
 
 ## [0.12.0] 2018-11-28