Add `rvm` completion spec

[Alan Syue]

Sanity checks

• My issue relates to a specific CLI completion spec (e.g. git checkout is missing options in git completion spec). If your issue is more general, please create your issue here: withfig/fig
• I have searched github.com/withfig/autocomplete/issues and there are no duplicates of my issue
• I would like to work on this.

What CLI tool does this relate to?

rvm

Which statement makes the most sense?

This completion spec does not exist

Issue Details

reference: https://rvm.io/

[Vatana]

can i take up on this

[Alan Syue]

can i take up on this

Sure!

[Vatana]

I've created a PR for this. Please check it. Thanks!