Update README.md

Include byte slice hexdump output in sample dump output.

README.md

@@ -62,6 +62,11 @@ spew.Fprintf(someWriter, "myVar3: %#v -- myVar4: %#+v", myVar3, myVar4)
   (string) "one": (bool) true
  }
 }
+([]byte) {
+ 00000000  11 12 13 14 15 16 17 18  19 1a 1b 1c 1d 1e 1f 20  |............... |
+ 00000010  21 22 23 24 25 26 27 28  29 2a 2b 2c 2d 2e 2f 30  |!"#$%&'()*+,-./0|
+ 00000020  31 32                                             |12|
+}
 ```
 
 ## Sample Formatter Output