add documentation note

src/progpy/data_models/lstm_model.py

@@ -24,6 +24,15 @@ class LSTMStateTransitionModel(DataModel):
 
  Most users will use the :py:func:`LSTMStateTransitionModel.from_data` method to create a model, but the model can be created by passing in a model directly into the constructor. The LSTM model in this method maps from [u_t-n+1, z_t-n, ..., u_t, z_t-1] to z_t. Past :term:`input` are stored in the :term:`model` internal :term:`state`. Actual calculation of :term:`output` is performed when :py:func:`LSTMStateTransitionModel.output` is called. When using in simulation that may not be until the simulation results are accessed.
 
+ .. note::
+ ProgPy must be installed with [datadriven] option to use LSTM model. either
+
+ pip3 install progpy[datadriven]
+
+ or (if using local version)
+
+ pip3 install '.[datadriven]'
+
  Args:
  output_model (keras.Model): If a state model is present, maps from the state_model outputs to model :term:`output`. Otherwise, maps from model inputs to model :term:`output`
  state_model (keras.Model, optional): Keras model to use for state transition