Added note to readme about Timber 2 support

Author: sdunham

README.md

@@ -48,6 +48,7 @@ Let's get one thing out of the way: Greg is **not** a drop-in replacement for Th
   * PHP >= 7.4
   * WordPress Core >= 5.5.1
   * [Timber 1](https://timber.github.io/docs/)
+    * If you need [Timber 2](https://timber.github.io/docs/v2/) support, use Greg v0.4.x
 
 ## Installation