[documentation] List of Eligible Domains is Out of Date

[Cameron Yick]

As of today, the link in the README.md returns a 404 error: https://opendata.socrata.com/dataset/Socrata-Customer-Spotlights/6wk3-4ija

I suspect an equivalent list of list of eligible domains might be in the response for this endpoint: https://socratadiscovery.docs.apiary.io/#reference/0/count-by-domain/count-by-domain?console=1

Suggested next steps

1. Find out if there's an updated Socrata view to link to instead
2. Updated README to point to somewhere in the Apiary docs instead of to the old link