Added git playground link (#4356)

free-programming-playgrounds.md

@@ -9,6 +9,7 @@
 * [Elm](#elm)
 * [Flutter](#flutter)
 * [GDScript](#gdscript)
+* [Git](#git)
 * [Go](#go)
 * [Haskell](#haskell)
 * [Ionic](#ionic)
@@ -86,6 +87,11 @@
 * [GDScript](https://gdscript-online.github.io)
 
 
+### Git
+
+* [Git](https://learngitbranching.js.org/?NODEMO)
+
+
 ### Go
 
 * [Go Playground](https://play.golang.org)