message: update bind README
diff: @@ -24,6 +24,7 @@ MessagePack encoded data is sent between module boundaries. Decoding of the mess
  | Boolean | bool | true or false stored as 1 byte. |
  | Bytes | bin 8/16/32 | array of 8-bit unsigned integer. |
  | BigInt | fixstr or str 8/16/32 | UTF-8 string. |
  +| JSON | fixstr or str 8/16/32 | UTF-8 string. |
  | [Type] | fixarray or array 16/32 | Array of elements. |
  | type CustomObject {<br/>&nbsp;&nbsp;prop: Type<br/>} | fixmap or map 16/32 | sdf |
  