More in-depth ScalaDoc for `\/`

I'm hoping to start adding to ScalaDoc descriptions that seem sparse as I encounter them. This is my first attempt.

I'm not quite sure of the right level of detail and what should be accomplished through blog posts, examples, etc. However, I think discoverability of Scalaz features is an issue currently (I've gotten this feedback from multiple sources), so I'd rather err on the side of too much detail than not enough.