Clarify package purpose and use cases

[naclomi]

The first few slides of your presentation in docs/ do a great job of explaining in a quick-to-the-point way what this package provides! The top of the github readme should reflect the same information. During a technology review it's the first (and possibly only) thing prospective users will see, but as is, the background paragraph doesn't make it clear this is a turn-key book recommendation engine a la Netflix or Goodreads.