docs: outline functionality in readme

Author: Greg Bowler

README.md

@@ -11,6 +11,19 @@ The file at `.github/workflows/ci.yml` shows how to use [php-actions/phpunit][ac
 
 Versions of PHPUnit and all options are available to configure. Please see the [php-actions/phpunit documentation][action-link] for more information! 
 
+Functionality
+-------------
+
+There are two classes in this example project; `Greeter` and `EnvGreeter`, in the `src/` directory, which are tested in the `test/` directory.
+
+The `Greeter` has a function, `greet()` which takes an optional name. Without providing a name, the Greeter will return "Hello!", otherwise it will include the provided name, like "Hello, Example!".
+
+The `EnvGreeter` extends `Greeter` and provides a new function, `greetFromEnv()`, which takes the name of an environment variable to load the name from.
+
+The GitHub Action tests are executed in the [`ci.yml` file](https://github.com/php-actions/example-phpunit/blob/e1db6474eec4dc75526042f9cf5dab2bf8f163f9/.github/workflows/ci.yml#L14-L21) where the TEST_NAME environment variable is declared, along with any other PHPUnit configuration.
+
+Click the [Actions tab](https://github.com/php-actions/example-phpunit/actions) at the top of this repository to view the latest test runs.
+
 *** 
 
 If you found this repository helpful, please consider [sponsoring the developer][sponsor].