Clarify why `"hej" == "hej"` sometimes evaluates to `true` in Java, i.e mention string interning in J.1.67 or J.1.68.

[EliasAAradsson]

See "Appendix J Introduktion till Java" slide J.1.67 and J.1.68 to see what I'm on about. Perhaps add this link: https://stackoverflow.com/questions/10578984/what-is-java-string-interning