SIaaflux needs a better description

[ifenty]

Currently:

      "name": "SIaaflux",
      "long_name": "Conservative ocean and sea-ice advective heat flux adjustment",
      "units": "W m-2",
      "comments_1": "Heat flux associated with the temperature difference between sea surface temperature and sea-ice (assume 0 degree C in the model)",
      "comments_2": "Note: heat flux needed to melt/freeze sea-ice at 0 degC to sea water at the ocean surface (at sea surface temperature), excluding the latent heat of fusion.",
      "direction": ">0 decrease potential temperature (THETA)",