flash reading and writing

[Wwing]

dear team:

 How to use nrfjprog to read and write data to flash at specified address

[ketiljo]

https://infocenter.nordicsemi.com/topic/ug_nrf5x_cltools/UG/cltools/nrf5x_nrfjprogexe_reference.html?cp=6_1_3_0

Use --memwr and --memrd