updating readme for tutorial series concept

Author: andrewjtech123

README.md

@@ -7,23 +7,36 @@ This repository is home to the code examples highlighted in various [Shopify API
 #### 01 Getting Started
 - Building a public Shopify application ([tutorial](https://help.shopify.com/api/tutorials/building-public-app))
 
-#### 02 - Charging For Your App
-- Billing API Tutorial ([tutorial](https://help.shopify.com/api/tutorials/adding-billing-to-your-app/))
+#### 02 - Adding billing to your app
+- Adding billing to your app ([tutorial](https://help.shopify.com/api/tutorials/adding-billing-to-your-app/))
+
+## Requirements
+
+* [Ruby](https://www.ruby-lang.org/en/documentation/installation/) (sample apps were written with Ruby 2.2.1)
+* [RubyGems](https://rubygems.org/pages/download), the package management tool for Ruby
+* [Bundler for Ruby](http://bundler.io/), a dependency manager
+
+## Installation
+
+* Download the sample code from the [this repo](https://github.com/Shopify/example-ruby-app)
+* To get the necessary dependencies, navigate to the application folder and type `bundle install`
 
 ## Credentials
 
-This example uses a `.env` file to store the application credentials. After cloning the repository, you'll need to create a file named `.env` in the same folder of the tutorial. The contents of the file should be as follows:
+To create a public app and retrieve your API credentials, sign up for a [Shopify Partners account](https://app.shopify.com/services/partners/auth/login) and [follow this guide](https://help.shopify.com/api/guides/api-credentials).
+
+This tutorial series uses a `.env` file to store application credentials.  For each installment in the series there is a corresponding app directory and `app.rb` file.  When following the tutorials, make sure the app directory includes a `.env` file with contents as follows:
 ```
 API_KEY=YOUR_API_KEY
 API_SECRET=YOUR_SECRET_KEY
 ```
 
 where `YOUR_API_KEY` and `YOUR_SECRET_KEY` are the values of your application's API key and secret key respectively.
 
-To retrieve your API credentials, sign up for a [Shopify Partners account](https://app.shopify.com/services/partners/auth/login) and [follow this guide](/api/introduction/getting-started).
+## App URL
+
+This tutorial series using [ngrok](https://ngrok.com/) to create a secure tunnel from the public Internet to your local machine.  For each installment in the series, you will need to copy the `APP_URL` generated by ngrok to your `app.rb` file.  Additionally, the `APP_URL` needs to be added to the **App URLs** section of your public app settings.  These procedures are covered in part one of the tutorials.
 
-## Running the app
+## Running the apps
 
-1. Create the `.env` file as described above.
-2. `bundle install` to obtain all of the necessary dependencies
-3. `ruby app.rb` to run the example application.
+Each installment of the tutorials includes an app.rb file inside the app directory.  To initialize an app, navigate to the correct app directory in terminal and then run `ruby app.rb`.