Add reminder about OpenJDK and OpenJFX in build instructions
Add reminder about OpenJDK and OpenJFX in build instructions

ManfredKarrer/exchange,sakazz/exchange,bisq-network/exchange,sakazz/exchange,ManfredKarrer/exchange,haiqu/bitsquare,haiqu/bitsquare,metabit/bitsquare,metabit/bitsquare,bitsquare/bitsquare,bisq-network/exchange,bitsquare/bitsquare