Added upgrade instructions for the audio board

README.md

@@ -1,3 +1,37 @@
 # Pico TinyUSB i2s Speaker
 
-A USB speaker firmware for the RP2040/Pico using TinyUSB and i2s.
+A USB speaker firmware for the RP2040/Pico using TinyUSB and i2s.
+
+## Updating the firmware for the board
+
+Push the volume button in for 2 seconds and hold.
+
+This will put the audio board into bootloader mode.
+
+If you're using Recalbox, you may see a pop up that states a new USB device named RPI-RP2 has been discovered and asks you if you wish to initialise.  You can ignore this screen.
+
+If you don't have any other external USB devices plugged in, you should be able to access the bootloader at:
+
+    /recalbox/share/externals/usb0
+
+If you have more than one device plugged in, check the USB folders for two files in here - one called INDEX.HTM and one called INFO_UF2.TXT
+
+The contents of INFO_UF2.TXT should be something like:
+
+    UF2 Bootloader v3.0
+    Model: Raspberry Pi RP2
+    Board-ID: RPI-RP2
+
+Using scp or windows explorer, you should be able to drag/drop the uf2 file from this repo there.  The audio board will apply the update and then restart itself.
+
+Check the releases page here for the latest link:
+
+https://github.com/pimoroni/picade-max-audio/releases
+
+If you want to double check, ssh to the picade and run
+
+    mount
+
+You're looking for an entry like this one - if you have a USB drive or other devices are in bootloader mode you might see more than one listed here.
+
+    /dev/sda1 on /recalbox/share/externals/usb0 type vfat (rw,sync,nodev,noexec,noatime,nodiratime,fmask=0022,dmask=0022,codepage=437,iocharset=ascii,shortname=mixed,errors=remount-ro)