Add an external import helper module

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

pimoroni_pico_import.cmake

@@ -0,0 +1,28 @@
+# This file can be dropped into a project to help locate the Pimoroni Pico libraries
+# It will also set up the required include and module search paths.
+
+if (NOT PIMORONI_PICO_PATH)
+    set(PIMORONI_PICO_PATH "../../pimoroni-pico/")
+endif()
+
+if(NOT IS_ABSOLUTE ${PIMORONI_PICO_PATH})
+    get_filename_component(
+        PIMORONI_PICO_PATH
+        "${CMAKE_CURRENT_BINARY_DIR}/${PIMORONI_PICO_PATH}"
+        ABSOLUTE)
+endif()
+
+if (NOT EXISTS ${PIMORONI_PICO_PATH})
+    message(FATAL_ERROR "Directory '${PIMORONI_PICO_PATH}' not found")
+endif ()
+
+if (NOT EXISTS ${PIMORONI_PICO_PATH}/pimoroni_pico_import.cmake)
+    message(FATAL_ERROR "Directory '${PIMORONI_PICO_PATH}' does not appear to contain the Pimoroni Pico libraries")
+endif ()
+
+message("PIMORONI_PICO_PATH is ${PIMORONI_PICO_PATH}")
+
+set(PIMORONI_PICO_PATH ${PIMORONI_PICO_PATH} CACHE PATH "Path to the Pimoroni Pico libraries" FORCE)
+
+include_directories(${PIMORONI_PICO_PATH})
+list(APPEND CMAKE_MODULE_PATH ${PIMORONI_PICO_PATH})