Add Java setup instructions (MacOS)

[koushikkothagal]

Add Java setup instructions here: https://github.com/koushikkothagal/java-backend-bootcamp/tree/main/session-02-big-picture#setting-up-java

Add step-by-step instructions and screenshots. Submit a PR when done

[ryanohcodes]

Hey Koushik, I would like this one as well. Please and thank you.

[koushikkothagal]

Done!