add a small note

README.md

@@ -55,6 +55,8 @@ jobs:
 
 [![Basic example](https://github.com/cypress-io/github-action/workflows/example-basic/badge.svg?branch=master)](.github/workflows/example-basic.yml)
 
+The workflow file [.github/workflows/example-basic.yml](.github/workflows/example-basic.yml) shows how Cypress runs on GH Actions using Ubuntu (16, 18, or 20), on Windows, and on Mac without additional OS dependencies necessary.
+
 **Note:** this package assumes that `cypress` is declared as a development dependency in the `package.json` file. The `cypress` NPM module is required to run Cypress via its [NPM module API](https://on.cypress.io/module-api).
 
 ### Explicit version