add docker image reference to phpcs-security-audit

Author: streichsbaer

README.md

@@ -32,6 +32,7 @@ Special thanks to: [GuardRails.io](https://github.com/apps/guardrails)
 ## Static Code Analysis
 
 - [phpcs-security-audit](https://github.com/FloeDesignTechnologies/phpcs-security-audit) - phpcs-security-audit is a set of PHP_CodeSniffer rules that finds vulnerabilities and weaknesses related to security in PHP code.
+    - `docker pull guardrails/phpcs-security-audit`
 - [progpilot](https://github.com/designsecurity/progpilot) - A static analyzer for security purposes.
 - [Parse](https://github.com/psecio/parse) - The *Parse* scanner is a static scanning tool to review your PHP code for potential security-related issues.