[ACELL01] Readme does not specify which HW configurations are supported

[aliphys]

The Arduino_Cellular library provides a way to interact with the Arduino PRO 4G EMEA (TPX00201) and GNSS (TPX00200) modules via the Arduino language. In the current form, there is no explicit mention of which hardware boards are compatible.

• 🤓 The instructions mention the Portenta Mid Carrier. This would imply that this library involves a combination of the Arduino PRO 4G module with the Portenta Mid Carrier.

  Arduino_Cellular/README.md

  Line 27 in 414d5e3

  1. Insert your Arduino 4G module to the [Arduino Portenta Mid Carrier](https://store.arduino.cc/collections/portenta-family/products/portenta-mid-carrier)

• 📡 The two examples mention GPS. It should be stated that this is only for the GNSS variant (TPX00200) to prevent false expectations.

  Arduino_Cellular/README.md

  Lines 11 to 12 in 414d5e3

  	* [GetLocation](examples/GetLocation) - Shows how to get the current GPS location.
  	* [GetTime](examples/GetTime) - Use GPS to acquire the time of the device.

• 📐 The Pro 4G GNSS and EMEA modules are PCIE devices and thus fit into the PCIE slot on the Portenta Max Carrier (SKU: ABX00043). However, at this time we do not support this as a configuration (the Portenta Max Carrier has a SARA-R412M-02B already on the board itself).
• 🐧 None of the library examples compile with the Portenta X8. Regardless, the OoB experience with the Portenta X8 does not involve the Arduino_Cellular library since network connectivity is provided by the Yocto Linux on this board. In other words, the Portenta X8, Portenta Mid Carrier and the Pro 4G EMEA/GNSS are compatible just not via Arduino_Cellular. This has been detailed in the Portenta X8 User Manual by @martab1994

As you can see, Portenta X8 features two powerful computing units:

* **NXP® i.MX 8M Mini** Cortex®-A53 quad-core up to 1.8GHz per core + 1x Cortex®-M4 up to 400 MHz. This microprocessor is the one where the Yocto Linux distribution is running together with Docker containers (check [this section](#linux-environment) of this user manual to learn more).

* **STMicroelectronics STM32H747XI** dual-core Cortex®-M7 up to 480 MHz + M4 32 bit Arm® MCU up to 240 MHz. This microcontroller is the one where the "Arduino Mbed OS Portenta Boards" Core is running. M4 core is accessible and programmable by the user, while M7 is dedicated to establishing and guaranteeing the communication between i.MX 8M Mini and M4 as well as to manage peripherals through RPC. Check [this section](#arduino-environment) of this user manual to learn more.

The two computing units are responsible for different tasks, which are summarized in the table below.

  | NXP® i.MX 8M Mini                                       | STMicroelectronics STM32H747XI (M4)                            |
  | ------------------------------------------------------- | -------------------------------------------------------------- |
  | Running Yocto Linux distribution with Docker containers | Running Arduino sketches with the Mbed OS Portenta Boards Core |
  | Dedicated to high level tasks                           | Dedicated to real-time tasks                                   |
  | Manage network connectivity                             | No direct connection to any network stack                      |
  | Manage network-based buses (e.g. Modbus TCP, etc.)      | Manage field buses (e.g. Modbus RTU, CANbus, etc.)             |
  | Access to peripherals without concurrent access control | Access to peripherals without concurrent access control        |

Merging https://github.com/arduino-libraries/Arduino_Cellular/pull/17/files partly address this issue, by expanding the setup instructions to mention C33 and H7 boards