update readme for osx
update readme for osx

pzduniak/protobuf-int64,chrisdew/protobuf,avail/protobuf-int64,pzduniak/protobuf-int64,JacksonTian/protobuf,chrisdew/protobuf,XadillaX/protobuf,XadillaX/protobuf,XadillaX/protobuf,chrisdew/protobuf,avail/protobuf-int64,pzduniak/protobuf-int64,avail/protobuf-int64,XadillaX/protobuf,XadillaX/protobuf,JacksonTian/protobuf,chrisdew/protobuf,pzduniak/protobuf-int64,avail/protobuf-int64,JacksonTian/protobuf,JacksonTian/protobuf,JacksonTian/protobuf,chrisdew/protobuf,avail/protobuf-int64,pzduniak/protobuf-int64