Improve usage instuction

[452]

I trying to build and don't know how to compile .java to .class files
and how to compile for esp32 and esp8266

Please provide instruction with information steps how to build binary for a specific platform(esp32, esp8266)

Also interested JVM implementation:
https://github.com/452/javaino-examples
Javaino

I have a sample board, looks good