Add message to avrdude script that it can't used within WSL currently

tmk_core/avr.mk

@@ -145,6 +145,9 @@ dfu-ee: $(BUILD_DIR)/$(TARGET).hex $(BUILD_DIR)/$(TARGET).eep
 	$(DFU_PROGRAMMER) $(MCU) reset
 
 avrdude: $(BUILD_DIR)/$(TARGET).hex
+	if grep -q -s Microsoft /proc/version; then \
+		echo 'ERROR: Pro Micros can not be flashed within the Windows Subsystem for Linux (WSL) currently. Instead, take the .hex file generated and flash it using AVRDUDE, AVRDUDESS, or XLoader.'; \
+	else \
 		ls /dev/tty* > /tmp/1; \
 		echo "Detecting Pro Micro port, reset your Pro Micro now.\c"; \
 		while [ -z $$USB ]; do \
@@ -156,7 +159,8 @@ avrdude: $(BUILD_DIR)/$(TARGET).hex
 		echo ""; \
 		echo "Detected Pro Micro port at $$USB"; \
 		sleep 1; \
-	avrdude -p $(MCU) -c avr109 -P $$USB -U flash:w:$(BUILD_DIR)/$(TARGET).hex
+		avrdude -p $(MCU) -c avr109 -P $$USB -U flash:w:$(BUILD_DIR)/$(TARGET).hex; \
+	fi
 
 # Convert hex to bin.
 flashbin: $(BUILD_DIR)/$(TARGET).hex