SDRAM Examples

I've noticed the Portenta_SDRAM library: https://github.com/arduino/ArduinoCore-mbed/tree/master/libraries/Portenta_SDRAM
But it does not have an examples folder. It would be very helpful if someone could post a basic read/write example for interacting with the external SDRAM.

Start by inspecting the Portenta_SDRAM library at libraries/Portenta_SDRAM and check how its public interface is used. Add an examples folder containing a basic external SDRAM read/write example, and confirm that the example demonstrates both operations with the library.

Written by the indexing model from the issue text.