Improve documentation for configuration of JRE for binary releases

• JRE v11 must be in the path or configured via the autofocus3-phoenix.ini file.

• Add corresponding entry here https://download.fortiss.org/public/projects/af3/help/af3_faq.html

• Revise "Software Downloads" sections at https://www.fortiss.org/en/results/software/autofocus-3 to reference the FAQ not only w.r.t. MacOS trouble shouting, but in general regarding installation hints.