Convert raw VWC to percentish

[nubbysaurus]

Modify raw Teros-12 VWC readout in example to instead print VWC as a percentage / 100.

[cjosephson]

@nubbysaurus can you say a little more on this?

Converting to percent requires specifying a calibration, which will be soil-specific....the RAW value output is more versatile and any calibration (including the 'generic' one) can be applied to it.

[nubbysaurus]

Ahh, understood. Could this be refactored as an option for streaming? Having the "mineral soil" VWC reporting live over a serial connection is useful feedback for our experiments (but this could also just be a one-off branch).