doc: add friflo-engine-ecs to the list of similar projects (#1108)

docs/md/reference.md

@@ -55,6 +55,8 @@ details.
     inspired archetype ECS with optional multithreading. 
   * [Entitas](https://github.com/sschmid/Entitas-CSharp): the ECS framework for
     C# and Unity, where _reactive systems_ were invented.
+  * [Friflo Engine ECS](https://github.com/friflo/Friflo.Json.Fliox/blob/main/Engine/README.md):
+    an Archetype ECS with focus on performance, cache locality and DX.
   * [LeoECS](https://github.com/Leopotam/ecs): simple lightweight C# Entity
     Component System framework.
   * [Svelto.ECS](https://github.com/sebas77/Svelto.ECS): a very interesting