Improve Heroku deployment instructions

Updates `README.md`:

* Use abbreviated buildpack names
* Instruct users to add the generated files to version control

README.md

@@ -251,14 +251,15 @@ Specifying a deployment strategy is only supported for applications that use the
 
 To configure your EmberCLI-Rails applications for Heroku:
 
-1. Execute `rails generate ember:heroku`
+1. Execute `rails generate ember:heroku`.
+1. Commit the newly generated files.
 1. [Add the NodeJS buildpack][buildpack] and configure NPM to include the
    `bower` dependency's executable file.
 
 ```sh
 $ heroku buildpacks:clear
-$ heroku buildpacks:add --index 1 https://github.com/heroku/heroku-buildpack-nodejs
-$ heroku buildpacks:add --index 2 https://github.com/heroku/heroku-buildpack-ruby
+$ heroku buildpacks:add --index 1 heroku/nodejs
+$ heroku buildpacks:add --index 2 heroku/ruby
 $ heroku config:set NPM_CONFIG_PRODUCTION=false
 $ heroku config:unset SKIP_EMBER
 ```