I can go into more depth here, as I am currently doing this.

For minera to show up as a network device on Multiminer, you need to be using either BFGMiner or CGMIner (or an equivalent). CPUMiner does not have the option to push the api across the network (so far as I can see, due to the lack of options available when CPUMiner is selected).

Link:
http://ocau.com/pix/4mpuh

Gridseed Farm is a Minera Instance on a RasPi B+