Add MKR GSM memory disclaimer

Author: karlsoderby

content/cloud/iot-cloud/tutorials/01.iot-cloud-getting-started/iot-cloud-getting-started.md

@@ -84,6 +84,8 @@ Connection through mobile networks can be considered in remote areas where there
 
 ***For more information, visit the [Arduino SIM page](https://store.arduino.cc/digital/sim).***
 
+***Note that connection via GSM is a memory intense operation, so there's not a lot of memory for the user application (around 2.6 kB). Using a lot of IoT Cloud variables may cause the sketch to run out of memory on the MKR GSM 1400 and make it crash.***
+
 ### ESP32 / ESP8266
 
 The Arduino IoT Cloud supports a wide range of third party boards based on the ESP32 and ESP8266 microcontrollers with support for Wi-Fi. To set them up, simply choose the **third party option** in the device setup.