Update free-courses-en.md (#3840)

* Update free-courses-en.md

Added game development section and courses

* Update free-courses-en.md

Removed non-course, corrected linter error

free-courses-en.md

@@ -14,6 +14,7 @@
 * [Data Science](#data-science)
 * [Databases](#databases)
 * [Deep Learning](#deep-learning)
+* [Game Development](#game-development)
 * [Git](#git)
 * [Go](#go)
 * [Haskell](#haskell)
@@ -174,6 +175,11 @@
 * [What is Deep Learning](https://www.udacity.com/course/deep-learning--ud730) (Udacity)
 
 
+### Game Development
+
+* [Unity Beginner Fundamentals](https://learn.unity.com/course/unity-beginner-fundamentals)(Unity Learn)
+
+
 ### Git
 
 * [Bento Git Learning Track](https://bento.io/topic/git) (Bento)