Bottom casing does not have access hole for pi pico button

[metalsp0rk]

If we ever need to flash new firmware to the Pi Pico, we'll have to disassemble the unit and remove the Pico from the housing. While this is technically non-destructive, with the exception of hot glue, it is tedious and a better solution would be to include an access hole that would allow a paper clip to actuate the firmware flash button from outside the casing.

I will handle this myself, I just want to note it down here so I don't forget to do it.