Refresh a lot of the copy

This includes some small and some larger(er) changes, which I'll call out specifically in a moment, but generally:

* Typos and wording (small)
* Bring some tech stuff up to date (small)
* Change a few things about the rails engineering job description (bigger)
My vague experience is that most teams use the version of Ruby and Rails that was current at the time they started, so this is showing hammering home that that's not how we do business.