Add individual .md files explaining each rule

[captbaritone]

https://github.com/wix/eslint-plugin-lodash3 can serve as a model.

[Garbee]

I was trying to figure out a good way of doing docs. The lodash setup seems like a good setup to follow.

It would also allow taking links out of the errors and put them into the doc files with more detail. So good win both ways.