Add sponsor message

Author: Greg Bowler

README.md

@@ -68,6 +68,6 @@ Current versions supported by this Action:
 
 If you require a specific version that is not listed here, please request them in the [Github issue tracker](https://github.com/php-actions/phpunit/issues)
 
-If you found this repository helpful, consider [sponsoring the developer][sponsor].
+If you found this repository helpful, please consider [sponsoring the developer][sponsor].
 
 [sponsor]: https://github.com/sponsors/g105b