Article on wrapping C libraries in Nim

[PMunch]

@cmc, not really. To build I just need `--passL:"-lcoap-3"` and that tells Nim 
where to find all the missing symbols introduced by Futhark and to require that 
dynamic library when it loads. You could of course also static link, or even 
compile the library into the code directly as I do for stb in the example.