Add documentation / example for lists.

[idyll]

It would be great if the documentation included an example like:

params do
  requires :tags, List[String]
end

as I had to do a bit of code spelunking to figure out how to allow for a list of strings.

[falood]

Hi @idyll

I have update it here and you can check test case for simple usage.

Leave me a message if you have any other questions, please.

[idyll]

Awesome. Thanks.