Check for pimoroni-pico next to the pico sdk, then next to the project. If neither exist, fail with an error that tells the user to set PIMORONI_PICO_PATH.
Part of the fix for the Pico Boilerplate breakage mentioned in pimoroni/pico-boilerplate#8
This file is included here for posterity and because it's existence is used to validate PIMORONI_PICO_PATH