I propose that the instructions on the Github wiki page for installing Loomio on a local machine specify the versions of Ruby and Rails on which Loomio is expected to run.
In the short term, hand-coding the recommended/supported version(s) of Ruby, Rails and even known good OS platforms into the install instructions would be helpful.
In the longer term, I (naively) wonder if there's a way for the Wiki page to pull the value(s) from the app Gemfile, or to have the value specified somewhere common to the Rails app and the wiki (i.e. keep it DRY)?
This is also important now as Ruby and Rails are both transitioning major versions. Perhaps a continuous build (Jenkins? Hudson!?) against various versions of Ruby and Rails would help keep developers informed of the status of the code, at least on major platform revisions?