YODA-T-64 Update example's README.md with instructions for setting up…

… the example and running the application

example/README.md

@@ -1,12 +1,39 @@
-# Example
+# Instructions for running this example
 
+First, create a `.env` file in this example directory with the following content:
 
-**Run**
+```bash
+API_KEY="your-app-api-key"
+USERNAME="your-app-username"
+```
 
-First, make sure to put your sandbox api key in `index.php`, then:
+Next, install the dependencies using [Composer](https://getcomposer.org):
 
 ```bash
 $ composer install
+```
+
+Finally, run the [PHP built-in server](https://www.php.net/manual/en/features.commandline.webserver.php):
+
+```bash
 $ php -S localhost:9090
-$ # open http://localhost:9090
-```
+```
+
+Open your browser and navigate to [`http://localhost:9090`](http://localhost:9090) to see the example in action.
+
+## Folder/File tree
+
+```bash
+.
+├── README.md # The example's README file.
+├── composer.json # The Composer file for the example.
+├── index.php # The entry point for the example.
+├── public # Contains the frontend files for the example.
+│   └── js
+│       └── main.js
+│   └── css
+│       └── style.css
+├── views # Contains the views for the example.
+│   └── index.php
+└── .env # The environment file where you add your credentials.
+```