Documentation: installing TruffleRuby in JVM mode from RVM

[mohamedhafez]

In the Readme, it does not specify how to install TruffleRuby in JVM mode from RVM. If that's not supported, perhaps the Readme could mention that?

[eregon]

Yes, RVM does not support TruffleRuby in JVM mode currently and given the complexity of RVM I didn't add it.
Although of course someone else could try adding it if they feel like it.

I don't really want to add this in the README because that section is meant to be concise.
It could be added in https://github.com/oracle/truffleruby/blob/master/doc/user/ruby-managers.md though.

IMO there are few reasons to use RVM these days.

You should be able to install truffleruby manually via these instructions:
https://github.com/oracle/truffleruby/blob/master/doc/user/installing-truffleruby.md
That can probably also be added to rvm via rvm mount or so, but rvm adds a bunch of overhead and extra stuff that I wouldn't recommend.