Added node requirement to README

Author: IjzerenHein

README.md

@@ -12,6 +12,8 @@ Sometimes, importing a single javascript library can drastically increase your b
 
 ## Usage
 
+**Make sure you have node 8 or higher installed.**
+
 Install as a dev dependency:
 
 	yarn add --dev react-native-bundle-visualizer
@@ -25,6 +27,8 @@ And run it:
 	npm install --save-dev react-native-bundle-visualizer
 	./node_modules/.bin/react-native-bundle-visualizer
 
+*requires node 8 or higher*
+
 ### Gitignore output files
 
 Additionally, add the haul generated `dist` and `.happypack` folders to your `.gitignore` file: