message: Example: Quad to SD: improve comments
diff: Created: Chip Audette, OpenAudio, May 2019
  Purpose: Write 4 channels of audio to SD based on serial commands
  - via USB serial or via BT serial
  + via USB serial or via BT serial.
  +
  + Writes to a single 4-channel WAV file. Can be opened in Audacity.
  MIT License. use at your own risk.
  */
  