Add Melrōse to "Who uses Expr?" section

Co-authored-by: Anton Medvedev <[email protected]>

Author: emicklei

README.md

@@ -164,6 +164,7 @@ func main() {
 * [keda.sh](https://keda.sh) uses Expr to allow customization of its Kubernetes-based event-driven autoscaling.
 * [Span Digital](https://spandigital.com/) uses Expr in it's Knowledge Management products.
 * [Xiaohongshu](https://www.xiaohongshu.com/) combining yaml with Expr for dynamically policies delivery.
+* [Melrōse](https://melrōse.org) uses Expr to implement its music programming language.
 
 [Add your company too](https://github.com/expr-lang/expr/edit/master/README.md)