CLC-3439 Adding suggestion to use theine for development

Documentation (and reference) for adding [theine](https://github.com/mrbrdo/theine) as a tool for development with CalCentral (and any other JRuby Rails projects)
@coyote , looks like there were some typos in these sentences. Most of them can be deleted, though, since I don't think the README needs evidence that it works. The README is more to explain how to install it and how to use it.

So instead of "It is not added the Gemfile, but should be available in the development directory…" and the timing log, maybe you could say how you install it and run it?

Also, if you're using it with RubyMine, it might be worth noting. (If you're not, I'll try that combo myself.)