updated docstring

sup3r/models/base.py

@@ -48,10 +48,12 @@ def __init__(self,
  discriminative model (spatial or spatiotemporal discriminator). Can
  also be a str filepath to a .json config file containing the input
  layers argument or a .pkl for a saved pre-trained model.
- loss : str
+ loss : str | dict
  Loss function class name from sup3r.utilities.loss_metrics
  (prioritized) or tensorflow.keras.losses. Defaults to
- tf.keras.losses.MeanSquaredError.
+ tf.keras.losses.MeanSquaredError. This can be provided as a dict
+ with kwargs for loss functions with extra parameters.
+ e.g. {'SpatialExtremesLoss': {'weight': 0.5}}
  optimizer : tf.keras.optimizers.Optimizer | dict | None | str
  Instantiated tf.keras.optimizers object or a dict optimizer config
  from tf.keras.optimizers.get_config(). None defaults to Adam.