Document how to set options

[Nuru]

The README documents a set of options to set, but not how to set them. Please document how to set the options or, if it is as simple as including them in the Kramdown options set, show an example.

Extra credit: show how to set options for the parser from Jekyll.

Proposal

Feel free to make these changes to the README, if they are correct, next time you update it (I do not want to submit a separate PR):

Usage:

require 'kramdown'
require 'kramdown-parser-gfm'

Kramdown::Document.new(text, input: 'GFM', gfm_quirks: ["no_auto_typographic"]).to_html

Using with Jekyll:
parser-gfm is the default in Jekyll. You do not need to specify input: "GFM" and you can pass options to it in the kramdown portion of your config file. For example:

kramdown:
   gfm_quirks: ["no_auto_typographic"]