Improve docs on SYSEX bit

keyboards/planck/keymaps/cbbrowne/Makefile

@@ -16,7 +16,7 @@ AUDIO_ENABLE = yes           # Audio output on port C6
 UNICODE_ENABLE = no         # Unicode
 BLUETOOTH_ENABLE = no       # Enable Bluetooth with the Adafruit EZ-Key HID
 RGBLIGHT_ENABLE = no        # Enable WS2812 RGB underlight.  Do not enable this with audio at the same time.
-API_SYSEX_ENABLE = no
+API_SYSEX_ENABLE = yes      # Enable SYSEX API (+5390)
 
 # Do not enable SLEEP_LED_ENABLE. it uses the same timer as BACKLIGHT_ENABLE
 SLEEP_LED_ENABLE = no    # Breathing sleep LED during USB suspend