added billing note

01 Lab 3 Async Code.md

@@ -70,6 +70,10 @@ Most RESTful APIs return their data as a string in JSON format. This format allo
 
 In this exercise you will learn how to extract information from complex _JSON_ data.
 
+The first step is to create a Google account and obtain an API key using [these detailed instructions](https://developers.google.com/maps/documentation/javascript/get-api-key).
+
+**Note: to complete this section you will will need to sign up with a payment card to check you are a vaild user. You won't be charged unless you upgrade your account**. If you are not happy to do this please skip the rest of this section and go directly to the **Modules and Callbacks** task.
+
 1. Run the script by entering `node addressFinder 'coventry'`, the address you are looking for needs to be enclosed in single quotes. Notice the result (lots of data).
 2. Open the `addressFinder.js` file and notice that the script requires at least three parameters. The user will need to enter an address to look up.
 3. The third parameter (index 2) contains the address to find.