Update CHANGELOG.md now that I have a PR number

Author: nickpelone

CHANGELOG.md

@@ -29,6 +29,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   (#[1216](https://github.com/nix-rust/nix/pull/1216))
 - Added `BindToDevice` socket option (sockopt) on Linux
   (#[1233](https://github.com/nix-rust/nix/pull/1233))
+- Added `EventFilter` bitflags for `EV_DISPATCH` and `EV_RECEIPT` on OpenBSD.
+  (#[1252](https://github.com/nix-rust/nix/pull/1252))
 
 ### Changed
 - Changed `fallocate` return type from `c_int` to `()` (#[1201](https://github.com/nix-rust/nix/pull/1201))