Clarify README.
Clarify README.

alexreisner/geocoder,brian-ewell/geocoder,malandrina/geocoder,guavapass/geocoder,FanaHOVA/geocoder,rayzeller/geocoder,TrangPham/geocoder,sjaveed/geocoder,AndyDangerous/geocoder,3mundi/geocoder,sideci-sample/sideci-sample-geocoder,GermanDZ/geocoder,tiramizoo/geocoder,mdebo/geocoder,andreamazz/geocoder,Devetzis/geocoder,donbobka/geocoder,eugenehp/ruby-geocoder,moofish32/geocoder,rdlugosz/geocoder,ankane/geocoder,davydovanton/geocoder,gogovan/geocoder-olleh,mveer99/geocoder,mehlah/geocoder,tortuba/geocoder,aceunreal/geocoder,rios1993/geocoder,gogovan/geocoder-olleh,epyatopal/geocoder,StudioMelipone/geocoder,jaigouk/geocoder-olleh,jaigouk/geocoder-olleh,jgrciv/geocoder,boone/geocoder