New INSTALL file

@seriousamlqz, @yzhang90, @grosu, please review
I would skip all this paragraph.  We don't want people to make modifications to JavaMOP anyway, and it does not sound good to tell that we don't have a binary available.  Actually, I think we should, asap.  The same way to allow people to download K as a binary, we should also allow people to download JavaMOP as a binary.  We don't really need an installer for an academic tool.  A zip containing everything should suffice.  Can you take a look at how it is done in K, and do the same?  Start from kframework.org.