Add high level descriptions about the supported features in JVM implementation

[jserv]

It would be great if we can provide some high level descriptions about the supported opcodes/features in our JVM implementation.
See the following for reference:

• https://github.com/JorthVM/JorthVM/blob/master/implementation.md
• https://github.com/TheCurle/Purpuri/blob/master/docs/docs/spec.md