Document advanced input-output example

[trevorhardy]

This example serves to show the variety of ways HELICS federates can connect to transfer data. At one point @trevorhardy intended to use it to record a series of videos where he did live-coding to show how to build and configure federates. That may or may not be a good idea any more but once the example is working (see #126), we can figure out the best way to document it.