Merge pull request #582 from mlodato517/ml-webpacker-docs

Add note for using yarn if using webpacker

README.md

@@ -37,6 +37,18 @@ Add the gem to your Gemfile.
 gem "i18n-js"
 ```
 
+#### Rails with [webpacker](https://github.com/rails/webpacker)
+
+If you're using `webpacker`, you may need to add the dependencies to your client with:
+
+```
+yarn add i18n-js
+# or, if you're using npm,
+npm install i18n-js
+```
+
+For more details, see [this gist](https://gist.github.com/bazzel/ecdff4718962e57c2d5569cf01d332fe).
+
 #### Rails app with [Asset Pipeline](http://guides.rubyonrails.org/asset_pipeline.html)
 
 If you're using the [asset pipeline](http://guides.rubyonrails.org/asset_pipeline.html),