Mention requestjs-rails in the installation steps

Author: marcelolx

README.md

@@ -4,6 +4,12 @@ Rails Request.JS encapsulates the logic to send by default some headers that are
 
 # Install
 
+## Rails Asset Pipeline
+
+Install the [requestjs-rails](https://github.com/rails/requestjs-rails) gem and follow the step described there.
+
+## Webpacker
+
 ### npm
 ```
 npm i @rails/request.js