code: static byte[] append(byte[] data, byte[] toAppend) {
  
          ByteArrayOutputStream stream = new ByteArrayOutputStream();
          try {
              stream.write(data);
              stream.write(toAppend);
          } catch (IOException e) {
              e.printStackTrace();
          }
          return stream.toByteArray();
      }
docs: append appends a byte array to an existing byte array
  
  @param data     the data to which we want to append
  @param toAppend the data to be appended
  @return a new byte[] of data + toAppend