Added note to 'README' that this branch also uses 'package.json'.

Author: maratbn

README

@@ -2,4 +2,4 @@ This branch contains example commits for building a minimalistic React front-end
 with Webpack 4, as outlined in the tutorial at
 http://maratbn.com/blogs/2018/06/25/minimalistic-react-webapp-webpack-4/
 
-This branch swaps Preact for React.
+This branch uses 'package.json' and swaps Preact for React.