README: Different branches for Godot versions

README.md

@@ -7,6 +7,9 @@ be used with [Godot Engine](https://godotengine.org), the open source
 Those demos are distributed under the terms of the MIT license, as
 described in the [LICENSE.md](LICENSE.md) file.
 
+**Note:**
+Master branch is compatible with the latest Godot version (currently 3.0). Use the appropriate branch for your Godot version, for example branch [2.1](https://github.com/godotengine/godot-demo-projects/tree/2.1) for Godot 2.1.x.
+
 ### Useful links
 
  - [Main website](https://godotengine.org)