- add a note as to why we have this very complicated Annotated system
- add a note as to why we have this very complicated Annotated
system

Change-Id: I7d4048b92fcd3a7c7630c43aa9390d983f447c0a

wujuguang/sqlalchemy,monetate/sqlalchemy,sqlalchemy/sqlalchemy,j5int/sqlalchemy,graingert/sqlalchemy,j5int/sqlalchemy,wujuguang/sqlalchemy,monetate/sqlalchemy,graingert/sqlalchemy,zzzeek/sqlalchemy