Add a description to each rule

It would be helpful to include the description property for each rule. Personally, I like to use a simple script which uses meta information such as the URL (which is included for this plugin's rules) and the description (which is not currently included) for each rule.

I would recommend copying the descriptions from the README.

More information about the properties of a rule can be found here: https://eslint.org/docs/developer-guide/working-with-rules#rule-basics

If this suggestion is supported, I would be happy to submit a pull request implementing it.