Add note to readme about adapter name when using DATABASE_URL
Add note to readme about adapter name when using DATABASE_URL

[References #500]

luke2237/oracle-enhanced,cdinger/oracle-enhanced,ifad/oracle-enhanced,yahonda/oracle-enhanced,yahonda/oracle-enhanced,Eric-Guo/oracle-enhanced,rsim/oracle-enhanced,ifad/oracle-enhanced,cdinger/oracle-enhanced,ifad/oracle-enhanced,umn-asr/oracle-enhanced,rshell/oracle-enhanced,umn-asr/oracle-enhanced,claptimes5/oracle-enhanced,luke2237/oracle-enhanced,umn-asr/oracle-enhanced,swaroopmurthy/oracle-enhanced,rshell/oracle-enhanced,rsim/oracle-enhanced