make it clear there is a PCB available that can be ordered with SD card slot pre soldered etc

[jerabaul29]

Hi @gauteh :)

I was discussing last week at the Uppsala wave meeting with some colleagues. There was quite a lot of interest for the OMB and the SFY drifters :) .

A comment / feedback I got: people thought it may be useful to make it clear regarding the sfy that a "turn key ready to order PCB" is available, how to order it, and how to assemble a buoy based on it - I got the feedback that they were not aware of this by just skimming through the repo, and that being aware of it would make the project more attractive as it is much easier to build sfy buoys :) .