Dead links in Readme

[bitrecycling]

The two links to the spring documentation in the readme are dead (lead to 404)

This is misleading and lowers trust in maturity or support of that version

https://github.com/spring-projects/spring-security-samples/tree/main/servlet/java-configuration/saml2/login/README.adoc

Links that are not working:

• SAML 2.0 Logout feature: https://docs.spring.io/spring-security/site/docs/5.6.0-SNAPSHOT/reference/html5/#servlet-saml2login-logout
• reference documentation https://docs.spring.io/spring-security/site/docs/5.6.0-SNAPSHOT/reference/html5/#servlet-saml2login-logout