Add note about cross compiling
Add note about cross compiling

tarm/serial,BarkingMouseStudio/goserial,mvbjrn/goserial,cesanta/serial,tarm/goserial,huin/goserial,jmore-reachtech/serial,haxpax/goserial,jbuchbinder/goserial,tajtiattila/serial,jaseg/goserial,argandas/serial,johnlauer/goserial,vonwenm/goserial