Adding GCM4 SD demo.

Adafruit_Grand_Central_M4_Express/GCM4_SD_Temperature_Logging_Demo.py

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+import time
+import adafruit_sdcard
+import microcontroller
+import board
+import busio
+import digitalio
+import storage
+
+# Setup the little red LED on D13
+led = digitalio.DigitalInOut(board.D13)
+led.direction = digitalio.Direction.OUTPUT
+
+# Connect to the card and mount the filesystem.
+spi = busio.SPI(board.SD_SCK, board.SD_MOSI, board.SD_MISO)
+cs = digitalio.DigitalInOut(board.SD_CS)
+sdcard = adafruit_sdcard.SDCard(spi, cs)
+vfs = storage.VfsFat(sdcard)
+storage.mount(vfs, "/sd")
+
+print("Logging temperature to SD card")
+# We're going to append to the file
+while True:
+    # Open file for append
+    with open("/sd/temperature.txt", "a") as file:
+        led.value = True  # Turn on LED to indicate we're writing to the file
+        temperature = microcontroller.cpu.temperature
+        print("Temperature = %0.1f" % temperature)
+        file.write("%0.1f\n" % temperature)
+        led.value = False  # Turn off LED to indicate we're done
+    # File is saved
+    time.sleep(1)