README.md: avoid []byte -> string allocation/copy (#98)
README.md: avoid []byte -> string allocation/copy (#98)

FreeCache invests a lot of effort to minimize GC overhead, yet the README example has a case where a (potentially very large) copy is made just as part of a `fmt.Println` call. With this change, it uses `fmt.Printf("%s\n", ...)`, which should be used in any case involving `Println` and a `[]byte` that's intended to be interpreted as string data.
coocood/freecache