Add a minimal calibration example

This commit adds two simple calibration tutorials, with detailed
explanations. We calibrate two parameters, g1 and g0, on
canopy transpiration data target, using EnsembleKalmanProcesses.jl.
We use a single site model, at the ozark site, and calibrate first on
simulation output, with the goal of demonstrating the ability to
recover the original parameters and demonstrate a simple calibration
framework. Then, in a second tutorial, we calibrate on actual
observation data.