Add Troubleshooting section.
Add Troubleshooting section.

Document uninitialized constant error with Mongoid.

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