Updating readme

Author: Andrew McLagan

README.md

@@ -49,3 +49,9 @@ For bug reports, please [open an issue on GitHub](https://github.com/rollbar/rol
 Tests are in `tests`.
 To run the tests: `composer test`
 To fix code style issues: `composer fix`
+
+## Docker
+Docker binaries are located in `./bin` and can be run by simply executing `bin/phpunit` for example.
+To run tests: `bin/phpunit`
+To run all supported versions: `bin/phpunit-versions`
+To run composer : `bin/composer install` OR `bin/composer update`