[doc] Additional rulesets are not listed in documentation

[adangel]

Affects PMD Version: since 6.46.0

Description:

In older versions, we e.g. show the quickstart ruleset and the old deprecated rulesets: https://pmd.github.io/pmd-6.45.0/pmd_rules_java.html#additional-rulesets

This is missing since 6.46.0, there is no section "Additional rulesets" anymore: https://pmd.github.io/latest/pmd_rules_java.html