Add changelog line

Author: volhovm

CHANGELOG.md

@@ -52,6 +52,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - bump itertools from 0.10.5 to 0.12.0 #1228
   ([#1228](https://github.com/o1-labs/openmina/pull/1228))
 
+### Other
+
+- Added a `flake.nix` for building the project on nixos/using nix ([#1241](https://github.com/o1-labs/openmina/pull/1241))
+
 ## [0.16.0] - 2025-04-04
 
 ### Added