Using code in modules

Placeholder page to fill out now that https://github.com/MovingBlocks/DestinationSol/pull/381 has been merged! The PR itself is sufficiently well documented to point out a lot of the involved details, partly we need to take some of that and place it here :-)

See also https://github.com/DestinationSol/Warp as the first code-bearing DS module.