add warning note on Cloud template limitations

add note one limitations on Template tutorial of number of things

Author: g-castronovo

content/arduino-cloud/10.education/02.templates/content.md

@@ -78,6 +78,8 @@ Templates can be imported easily by clicking on the import button from the templ
 
 Below the `Import Button`, you can find information on how many [Things](https://docs.arduino.cc/arduino-cloud/cloud-interface/things), [Variables](https://docs.arduino.cc/arduino-cloud/cloud-interface/variables) and [Dashboards](https://docs.arduino.cc/arduino-cloud/cloud-interface/dashboard-widgets) are associated with this template. The Arduino Cloud platform will handle the creation of these IoT components along with setting up the device and network for the selected template. 
 
+***Note: with a Free Plan a user can only have two Things at same time. When you already have two Things, you won't be able to click on IMPORT TEMPLATE. To avoid this you could choose to upgrade your Cloud plan or manually delete an existing Thing***
+
 ![Template creation](assets/template-creation.png)
 
 This process involves creating the necessary components and uploading the sketch (program) to your device: