Update README with CVE-2025-66475 reference

Author: pitbulk

README.md

@@ -8,6 +8,8 @@ Add SAML support to your PHP software using this library.
 Warning
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+Version 4.3.1 updates xmlseclibs to 3.1.4 due [CVE-2025-66475](https://github.com/advisories/GHSA-c4cc-x928-vjw9)
+
 This version is compatible with PHP >=7.3 and 8.X and does not include xmlseclibs (you will need to install it via composer, dependency described in composer.json)
 
 Security Guidelines