Change README's list of Dash data types link

[aaronkelton]

Under the "dashing.json Format" header in the README file, it says: "The list of Dash data types can be found here: https://kapeli.com/docsets."

Can we make this link more specific? E.g. "The list of Dash data types can be found here: https://kapeli.com/docsets#supportedentrytypes"