Add CI build status badge to README

Author: aka411

README.md

@@ -1,4 +1,5 @@
 # ECS Engine
+[![CI Build Status](https://github.com/aka411/ecs-engine/actions/workflows/ci.yml/badge.svg)](https://github.com/aka411/ecs-engine/actions/workflows/ci.yml)
 A custom-built **Entity Component System (ECS)**, originally developed as a subsystem for a game engine project I was working on.
 
 After creating a minimum working prototype, I decided to move the ECS into its own dedicated repository where I can easily develop it as a standalone project.
@@ -72,4 +73,4 @@ ecsEngine.addComponentToEntity(player, Velocity{10.0f, 1.0f, 0.0f});
   }
 
 ```
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