[Docs] Blockwise example

[DavidMarquezF]

Including an example of blockwise for the client and server or a brief explanation on how to use it in the README would be beneficial to get started, since it is a feature that will be used a lot in constrained networks.

[nkt-dk]

Hello,

Does anyone have a simple example how to use blockwise transfer on the server side? I have a RTOS based client that is able to communicate with the server using normal CoAP packets, but I struggle to understand how the server handle function can process a blockwise transfer request and send the appropriate amount of data.

Thanks!