readme tweaks

Author: mpstenson

README.md

@@ -211,14 +211,6 @@ composer test
 
 Please see [CHANGELOG](CHANGELOG.md) for more information on what has changed recently.
 
-## Contributing
-
-Please see [CONTRIBUTING](CONTRIBUTING.md) for details.
-
-## Security Vulnerabilities
-
-Please review [our security policy](../../security/policy) on how to report security vulnerabilities.
-
 ## Credits
 
 - [Matt Stenson](https://github.com/mpstenson)