Part of #1139

• More concrete examples/use cases, e.g. -min cli parameter - "How to use PMD"
• "I want to use PMD. I use maven. How?" (or ant or maven)
  Create specific PMD Example Projects - https://github.com/pmd/pmd-examples
  Similar what JUnit does: https://junit.org/junit5/docs/current/user-guide/#overview-getting-started-example-projects
• "I want to use maven site to generate a pmd report for Apex - how?" -> [apex] Maven site report #2564
• "I want to use different rulesets for the main code and for the test code"
• "I have some generated source that I don't want to check"
• "I want to have a nice html report and a xml report for further tooling"
• "I want to have my build failing for severe violations only, but still want
  to have all violations in the generated report"
• Show cases, sample reports: That could be: "look, that's the result when
  you run PMD with the quickstart ruleset against this open source project..."
  We had this once...: https://pmd.sourceforge.io/scoreboard.html
• Update the footer to add links to the "getting help" page