update README: add fdsys/bill_versions scrapers, remove info on the github hosted download files which no longer exist
update README: add fdsys/bill_versions scrapers, remove info on the github hosted download files which no longer exist

chriscondon/billtext,sunlightlabs/congress-opencongress,chriscondon/billtext,Nolawee/congress,Nolawee/congress,sunlightlabs/congress-opencongress,unitedstates/congress,boblannon/congress,unitedstates/congress,boblannon/congress