Add instructions for adding a city to the site

[groovecoder]

I'm not sure how to get Tulsa added to https://codeforamerica.github.io/PoliceOpenDataCensus/ ... There should be instructions on the site tell me how to add our city.

[creade]

Hey! Thanks so much for adding Tulsa's Complaint Data. I added some details to our readmes for people who don't come to us through the site. Any suggestions for clarifying the addition process on the actual page?