Add note about webpack versions

Author: danez

README.md

@@ -19,6 +19,10 @@ __Notes:__ Issues with the output should be reported on the babel [issue tracker
 
 <h2 align="center">Install</h2>
 
+> webpack 1.x | babel-loader <= 6.x
+>
+> webpack 2.x | babel-loader >= 7.x (recommended) (^6.2.10 will also work, but with deprecation warnings)
+
 ```bash
 yarn add babel-loader babel-core babel-preset-env webpack --dev
 ```