documentation walkthrough device with non-standard meassurement

## Expected Behavior
I do not manage to get a sensor running that does not meassure the standard values tempereature and humidity according to the documentation as it is now

## Actual Behavior
have a documentation in a way where it is easy to see how to setup AND send data to sensorlogger that is non-standard. In my case I would like to have a 3rd value voltage to control the battery. I would like to have that in the data list but don't see how to do that.

From the docu I can learn how to register a device with whatever value but I do not see how to send data afterwards.