Polling fallback message help

Motivated by: #284. [ci skip]
Good question! IIRC, I installed rvm directly via it's command line installation instructions.

There's some good info [here on managers and installers](https://www.ruby-lang.org/en/documentation/installation/) …

Maybe we could just say:

> 1. Upgrade [Ruby](https://www.ruby-lang.org/en/documentation/installation/) and [RubyGems](https://rubygems.org/pages/download).