Update README.rdoc
Update README.rdoc

add note about S3 compatibility
Sergey-B/rich,Sergey-B/rich,keithpops/rich,dalpo/rich,donbobka/rich,m-andreas/rich,artemaminov/rich,Nimdis/rich,donbobka/rich,kreativgebiet/rich,Nimdis/rich,artemaminov/rich,andora/rich,jerefrer/rich,dalpo/rich,m-andreas/rich,kreativgebiet/rich,andora/rich,donbobka/rich,Nimdis/rich,dalpo/rich,krim/rich,m-andreas/rich,jerefrer/rich,krim/rich,jerefrer/rich,kreativgebiet/rich,keithpops/rich,krim/rich,artemaminov/rich