Adds requirements information

It should cover everything a fresh install needs to get Encyclopedia running.

Gemfile changes: I ran into an odd SASS issue on 3.3.x which was fixed by using 3.2.x. None of the dependents of sass need > 3.2.x, so I just added the version specification.

I removed foreman from the Gemfile on [this](https://github.com/ddollar/foreman) recommendation:
> Ruby users should take care not to install foreman in their project's Gemfile.