Include enabling chunked downloads as a step [HC-1635] (#491)

* Include enabling chunked downloads as a step

* Include all relevant Mbed OS boards for chunked downloads tip

* Update content/Arduino Cloud/Cloud Editor/If-you-see-an-error-when-performing-an-Over-the-Air-OTA-upload.md

Co-authored-by: Per Tillisch <accounts@perglass.com>

* fix typos in comment

---------

Co-authored-by: Per Tillisch <accounts@perglass.com>

Author: seaxwi

content/Arduino Cloud/Cloud Editor/If-you-see-an-error-when-performing-an-Over-the-Air-OTA-upload.md

@@ -95,6 +95,7 @@ Follow these steps:
 1. Ensure the device is connected to a stable and uninterrupted power source.
 1. Upload a simple example sketch (such as BareMinimum) to prevent any resets caused by faulty code.
 1. If you're unable to program the device, try putting it in bootloader mode.
+1. If you’re using an Opta, Portenta H7, or Portenta C33 and connecting over Ethernet, enable chunked downloads by adding `ArduinoCloud.setOTAChunkMode();` to the `setup()` function in your sketch, immediately after the line `ArduinoCloud.begin(ArduinoIoTPreferredConnection);`.<!-- NOTE: The ethernet network stack can become unresponsive downloading the OTA file, resulting in the sha256 error. The chunked download was developed as a possible workaround for Opta, but it applies to all Mbed OS boards using Ethernet connection. It can also be enabled when connecting over Wi-Fi, but no improvement has been observed in these cases. -->
 
 ### SHA256 Unknown - Unknown Firmware detected after restart. {#sha256unknown}