docs: requires dc-v5

[gordonwoodhull]

I think the README should mention that this requires dc-v5 and how to get it, and possibly link to dc-js/dc.js#1801 for the example.

[kum-deepak]

Thanks, @gordonwoodhull. I will update this. Currently, I am almost ready for the alpha of the new version. Once done, there should be an npm alpha release. I will target to update these instructions after that.