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)
RabbitMQ isn't something related to testing & CI, so remove it and creating a new section as seen here.  Another place where we emphasize that while we're effective and get things done, we aren't all-knowing, and that this is a specific thing a good candidate could help us with.