Merge pull request #151 from Shopify/feature/add-sample-readme

Add Customer Sample App README.md

Mobile Buy SDK Sample Apps/Sample App Customers/README.md

+# Mobile Buy SDK Customer Sample App
+
+The Customer Sample App demonstrates how to perform several tasks using the customer API.
+
+- Login customer
+- Create customer account
+- Fetch customer orders
+
+### Configuration
+
+First, configure the application with your shop domain, API key and app ID.
+
+```swift
+let shopDomain: String = ""
+let apiKey:     String = ""
+let appID:      String = ""
+```
+
+### Overview
+
+The Customer Sample App demonstates the usage of the customer API that lets you create a customer account, login with a customer account and show customer's orders after authentication.